Ma `lumot

Bu gullaydigan o'simlikmi?


Men do'stimdan sovg'a sifatida kichik bir o'simlik oldim.

Mana uning bargi:


Men uni Hindiston gullariga qarashga harakat qildim, lekin ularning ma'lumotlar bazasi qo'lda o'qish uchun juda ko'p.

Jismoniy tavsif:

Bu qisqa, taxminan 5 dyuym, ehtimol mening tajribamga ko'ra gullaydigan o'simlik (Uning aytishicha, bu kaktus, lekin men bunday deb o'ylamayman). Barg 1,5 sm atrofida va konus+silindrsimon tuzilishga ega.

Bu o'simlik qaysi turdagi va u gullaydiganmi?


Har qanday yordam ajoyib bo'lardi.


Crassula tetragona, shuningdek, mini qarag'ay daraxti sifatida ham tanilgan (bonsai texnikasida haddan tashqari foydalanish uchun), vatani Janubiy Afrika.

Bu shirali; suv saqlash uchun evolyutsiya natijasida hosil bo'lgan go'shtli barglari bilan ajralib turadigan kserofit (omon qolish uchun juda kam suvga muhtoj o'simlik), bu o'simlik 3 metrgacha balandlikka etadi.


Bu o'simlikda gullash odatda yoz mavsumida sodir bo'ladi, gullari sarg'ish to'q sariq va oq rangga ega.


Bu juda o'zgaruvchan turlarga o'xshaydi Kotiledon orbiculata. Ehtimol, flanaganii o'zgarishi.

Agar bu to'g'ri bo'lsa, sizning o'simlik juda gullab -yashnamoqda. Uning vatani Janubiy Afrika bo'lganligi sababli, uyingizda yoki bog'ingizda uning gullariga guvoh bo'la olasizmi, bilmayman.

Qanday bo'lmasin, uy hayvonlarini uzoqroq tuting, chunki ko'pchilik (shu jumladan itlar) bu o'simlikni yutganda zaharli ekanligini isbotlagan.


Gullaydigan o'simlikning hayot aylanishi

Gullaydigan o'simlikning hayot aylanishi urug 'bilan boshlanadi. Urug‘i unib, ko‘chat hosil qiladi, u o‘simlik bo‘lib yetiladi. Bu o'simlik keyinchalik yangi urug'lar hosil qilib ko'payadi va keyingi hayot tsiklini boshlaydi Quyidagi maqolada gulli o'simlikning hayot aylanishi haqida batafsil ma'lumot berilgan.

Gullaydigan o'simlikning hayot aylanishi urug'dan boshlanadi. Urug‘i unib, ko‘chat hosil qiladi, u o‘simlik bo‘lib yetiladi. Bu o'simlik keyinchalik yangi urug'lar hosil qilib ko'payadi va keyingi hayot tsiklini boshlaydi Quyidagi maqolada gulli o'simlikning hayot aylanishi haqida batafsil ma'lumot berilgan.

Siz o'zingizning uyingizda va atrofida chiroyli gullaydigan o'simliklar etishtirishni yaxshi ko'rishingiz kerak. Ular o'zlarining xushbo'y hidlari bilan atrof-muhitni tetiklashtiradi, shuningdek, atrofga juda maftunkor ko'rinish beradi. Gullaydigan o'simlikning hayot aylanishi bir necha bosqichlardan iborat. Biroq, ularning hayot aylanishini o'rganishga kirishishdan oldin, ularning tuzilishini o'rganish kerak.

Tuzilishi

Bizga yozmoqchimisiz? Xo'sh, biz so'zni tarqatishni xohlaydigan yaxshi yozuvchilarni qidirmoqdamiz. Biz bilan bog'laning va biz gaplashamiz.

Ildiz, poyasi, barglari, gullari va mevalari har qanday gullaydigan o'simlikning asosiy qismidir. Ildiz tizimi haqida gapiradigan bo'lsak, asosiy ildiz/ ildiz tagida lateral ildizlar va ildiz tuklari deb nomlanuvchi bir nechta novdalar mavjud. Ildizlar tuproqda chuqur o'sadi va ularning asosiy vazifasi tuproqdan suv va mineral tuzlarni o'zlashtirishdir. Kurtaklar tizimiga poya, barglar va gullar kiradi.

Poyasi yer yuzasidan oʻsadi va bir nechta shoxlari bor. Uning asosiy vazifasi suv va minerallarni ildizdan boshqa qismlarga tashishda yordam berish va yordam berishdir. Barglar fotosintez jarayonida muhim rol o'ynaydi, bu o'simlik o'sishi uchun hal qiluvchi jarayondir. Gullar o'simlikning ko'payishi uchun zarurdir, chunki ular changlatuvchilarni jalb qilishga yordam beradi.

Hayot tsikli: umumiy nuqtai

Gulli o'simliklar (angiospermlar) qon tomir o'simliklar bo'limiga kiradi, Anthophyta. Gullar va urug 'beradigan mevalar ularning ko'payish organlari hisoblanadi. Erkak stamen va ayol pistil kabi jinsiy a'zolar turiga qarab gullar biseksual yoki bir jinsli bo'lishi mumkin. Bitta o'simlikda alohida erkak va urg'ochi gullari bo'lgan turlar bir jinsli, har xil o'simliklarda urg'ochi va erkak gullari alohida turlar deyiladi. ikkilamchi.

Ayol pistilasi bitta yoki ko'p karpelli stigma, uslub va tuxumdondan iborat. Erkak stamen polenli anter va poya yoki filamentdan iborat. Quyidagi fikrlar changlanish jarayonini tushuntiradi.

  • Tuproqda yotgan uxlab yotgan urug' gullaydigan o'simlikka aylanishi uchun kislorod, suv va qulay o'sish sharoitlarini talab qiladi. Erda yotgan ba'zi urug'lar qulay muhitga ega bo'ladi va etuk o'simlik bo'lib o'sadi.
  • Urug'ga etarli miqdorda kislorod va suv berilsa, u unib chiqa boshlaydi. Niholning birinchi belgisi - ildizlarning tuproqqa o'sishi. Shundan so'ng, poyaning o'sishi yorug'lik tomon yuqoriga qarab boshlanadi.
  • Poyasi uzluksiz o'sadi, barglari va gullarini ko'taradi.
  • Yetuk gullar o'simlikning ko'payishini ta'minlaydigan qismlarni o'z ichiga oladi. Changlatish o'simliklarning ko'payishida hal qiluvchi rol o'ynaydi. Polen turli xil vositalar yordamida tarqaladi, masalan, hasharotlar, shamol, qushlar va boshqalar.
  • Keyingi qadam urug'lantirisherkak va urg'ochi jinsiy hujayralarning birlashishi. Stigma tushgandan so'ng, ikki yadroli polen donasi o'sib chiqadi va polen naychasini rivojlantiradi. Polen naychasi tuxumdonga o'sib boradi. Tuxumdonda u tuxumdonga mikropil orqali kiradi (tuxumdon devorida ochiladi).
  • Gulli o'simliklar polen naychasidan ikkita spermani o'z ichiga olgan er -xotin urug'lanishni ko'rsatadi. Bir spermatozoid tuxum bilan birlashib, diploid zigota hosil qiladi, ikkinchisi esa ikkita qutb yadrosi bilan birlashib, triploid endospermni rivojlantiradi.
  • Zigota embrionga aylanadi va embrionni o'rab turgan oziqlantiruvchi to'qima endospermdan hosil bo'ladi. Bu jarayonda tuxumdon hajmi kattalashib, etuk urug'ga aylanadi. Tuxumdonning tashqi ikki qatlami urug' qobig'ini hosil qiladi.
  • Pishgan tuxumdon meva sifatida tanilgan, u quruq yoki go'shtli bo'lishi mumkin. Meva quriganida va urug'lar ochilganda, ular hasharotlar, hayvonlar, qushlar yoki shamol tomonidan tarqalib ketadi.
  • Urug'langan urug'lar erga tushadi va bir xil hayot aylanishi boshlanadi.

Umid qilamanki, yuqoridagi ma'lumotlar gullaydigan o'simlikning hayot aylanishini aniqlashda sizga yordam berdi.

Tegishli xabarlar

Hammamizga ma'lumki, Yerdagi hayot manbai Quyoshdir. Ammo bilasizmi, fotosintezsiz, Quyoshdan olingan energiya isrof bo'ladi

Ko'pchilik nazarida klonlash kabi odatlar haqida gapirganda, gen muhandisligi etikasini bilib oling, ijodga axloqsiz va buzuq hujum.

Tabiatning eng qiziqarli hodisalaridan biri bo'lgan fotosintez bosqichlari haqida ko'proq bilish uchun o'qing.


  • IAA (auksin) kurtakning apikal meristemasida hosil bo'ladi.
  • Bu poyaning soyali tomoni bo'ylab tarqaladi.
  • Bu soyali tomonda hujayra uzayishiga olib keladi.
  • Ildizning soyali tomoni poyaning ochiq tomoniga qaraganda tezroq o'sadi.
  • Bu kurtakning yorug'lik manbasiga egilishiga olib keladi.
  • Naftalin sirka kislotasi (NAA) tijorat ildiz kukuni sifatida ishlatiladi.
  • Eten meva pishadigan vosita sifatida ishlatiladi.

Gullaydigan o'simlikning tuzilishi

Barcha gullaydigan o'simliklar deyiladi angiospermlar.

O'simliklar ikki guruhga bo'linadi:
1. Bir pallali
2. Ikki pallali

O'simlikning erta rivojlanish davrida kotiledonlar oziq -ovqat manbai sifatida yoki fotosintez uchun ishlatiladi (o'simlik turiga qarab).

Monokotiledonli o'simliklar bitta embrion urug 'bargiga ega.
Ikki pallali o`simliklar ikkita embrion urug` bargiga ega.

Gulli o'simliklardagi to'qimalar turlari:
1. Dermal: tashqi qoplama – himoya qilish, gaz almashinuvi yoki suv va minerallarni singdirish funktsiyalari (uning joylashishiga qarab).
2. Tuproq: fotosintez, saqlash yoki qo'llab-quvvatlash (uning joylashuviga qarab) o'simlik – funktsiyalarining asosiy qismini tashkil qiladi.
3. Qon tomir: ksilema va phloem to'qimalaridan tashkil topgan & suv va mineral transport (ksilem) va oziq -ovqat transportida (phloem) funktsiyalari.
4. Meristematik: yuqoridagi uch turdagi to'qimalarning har birida rivojlanadi.

  • Meristem: tez bo'linadigan maxsus bo'lmagan hujayralardan tashkil topgan o'simlik to'qimasi. Bu hujayralar mitoz yo'li bilan bo'linadi.

Gullaydigan o'simlikning tuzilishi

Diagrammada oddiy gullaydigan o'simlikning tuzilishi ko'rsatilgan.

Barcha o'simliklar ildiz tizimi va kurtaklar tizimidan iborat.

Otish tizimi:

Otish tizimi quyidagi organlardan iborat: poyasi, novdalari, barglari, kurtaklari, barglari, gullari, urug'lari va mevalari.

Otish tizimining funktsiyalari quyidagilardan iborat:

  • fotosintez
  • Qo'llab -quvvatlash
  • Transport
  • Jinsiy ko'payish
  • Oziq -ovqat mahsulotlarini saqlash
  • Gaz almashinuvi

Poyasi:

Poyasi asosan qo'llab-quvvatlash va tashishda ishlaydi, lekin fotosintezda (agar u o'tli bo'lsa) ishlay oladi. Poya ham o'sishda ishlaydi.
Poyasi bo'linadi tugunlar va internodlar.

Poyasi ham bor lenticels.

Yozuvlar:

Poyaning ichki tuzilishi:

Poyaning tuzilishi monokotlar va dikotlardan farq qiladi (quyida keltirilgan diagrammalarga qarang va kattaroq ko'rinishni ko'rish uchun har bir diagramaga bosing.

  • Monokotlarda poyaning ko'ndalang kesim tuzilishi:
  • Dikotdagi poyaning ko'ndalang kesim tuzilishi:
  • Dikotning uzunlamasına kesma tuzilishi:

Barg:

  • Yupqa organ katta sirt maydoniga ega.
  • O'simlik uchun oziq -ovqat tayyorlaydigan va transpiratsiya (o'simlikdan suv yo'qotilishi) funktsiyasini bajaruvchi organ.
  • Yashil pigment, xlorofillni o'z ichiga oladi.
  • Tashqi teri qatlami ortiqcha suv yo'qotilishining oldini olish uchun mumsimon kesikulani chiqaradi.
  • Bargda ko'plab ichki havo bo'shliqlari mavjud bo'lib, ular gaz almashinuvi uchun katta sirt maydoni beradi.
  • Barg ichidagi tuproq to'qimalarining yuqori qatlamini tashkil etuvchi hujayralarda fotosintezni amalga oshiradigan ko'plab xloroplastlar mavjud.
  • Pastki epidermis qatlamida stomata deb ataladigan ko'plab teshiklar mavjud.
  • Stomatal ochilish va yopilish himoya hujayralari tomonidan boshqariladi.

Barglarning tashqi va ichki tuzilishi:

  • Barglarning tashqi tuzilishi
  • Barglarning ichki tuzilishi

Barglarning chiqishi:

Barglardagi tomirlar ikki xil:

  • Tomirlar parallel ishlaydi, bargning butun uzunligi, masalan. o't, lola, za'faron.
  • Ko'pgina monokotli o'simliklar parallel venaga ega.
  • Tomirlar o'rta tomir deb ataladigan markaziy venadan tarqaladi (yuqoriga qarang).
  • Dikotli o'simliklarning ko'pchiligi to'rli yoki to'rli venatsiyaga ega.

Bud:

Kurtaklarning uch turi mavjud:

  1. Qo'ltiq osti kurtaklari: barg oqida joylashgan (poyasi bilan tokchasi o'rtasida).
  2. Apikal kurtak: o'simlikning uchida yoki novdaning uchida mavjud.
  3. Ajablanarlisi kurtak: o'simlikning g'ayrioddiy maydonida mavjud, masalan, poyasi, novdasi, ildizi yoki hatto barglari.
  • Qo'ltiq osti kurtaklari
  • Apikal kurtak
  • Ajablanarlisi kurtak

Monokotlar va dikotlar orasidagi gullar

  • Monokotlarda uch qismdan iborat gul qismlari bor.
  • Dikotalarning gul qismlari to'rt yoki beshga ko'paytiriladi.
  • Monokot gul
  • Dikot gullari

Ildiz tizimi:

Turli funktsiyalarga ega bo'lgan er osti filiallari tarmog'i:

  • Ankraj
  • Suv va minerallarni yutish
  • Olingan suv va minerallarni otish tizimiga tashish
  • Oziq -ovqat mahsulotlarini saqlash
  • Qo'llab -quvvatlash

Ildiz tizimining turlari:

  1. Ildiz tizimiga teging: kichik ildizlar bilan pastga qarab o'sadigan bitta asosiy ildiz, masalan. sabzi, momaqaymoq.
  2. Tolali ildiz tizimi: teng o'lchamdagi asosiy ildizlar, masalan. o't
  3. Noodatiy ildiz tizimi: poya yoki novdalar kabi g'ayrioddiy joylarda o'sadigan ildizlar, masalan. bayan daraxti, ivy.
  • Ildizga (momaqaymoq) teging
  • Tolali ildiz (marigold)
  • Sarguzasht ildizi (ivy)

Ildiz tuzilishi:

Yosh ildizning to'rtta zonasi bor.

  1. Himoya zonasi: ildiz qopqog'idan iborat bo'lib, ildizning erdan o'tishiga imkon beradi.
  2. Meristematik zona: mitoz orqali tez bo'linadigan, yangi ildiz to'qimasini hosil qiluvchi meristematik to'qimalardan iborat.
  3. Cho'zilish zonasi: o'sish regulyatorlari ta'sir qiladigan ildiz maydoni, bu erda hujayralar hajmi kattalashadi.
  4. Differensiallanish zonasi: ildizning ixtisoslashgan bo'lmagan hujayralar, tuproq, teri va qon tomir to'qimalarga aylana boshlagan sohasi.

Ildizning ko'ndalang tuzilishi quyida ko'rsatilgan:

Qon tomir tizimi

O'simlikning qon tomir tizimi ikki xil to'qimalardan iborat: ksilema va floema.


Gullar evolyutsion rivojlanish edi, bu o'simlik dunyosining turlarning xilma -xilligiga bom bo'lishiga imkon berdi. Ular ko'payishning muqobil usuli sifatida ishlab chiqilgan va juda muvaffaqiyatli ekanligi isbotlangan.

Meva barcha angiosperm o'simliklarida uchraydi va gul changlanishidan keyin hosil bo'ladi. Ular turli xil ranglar, shakllar va o'lchamlarda keladi.

6 haftalik BEPUL kurs

Elektron pochta orqali biologiyaga 6 haftalik BEPUL kirish kursimizga kirish uchun maʼlumotlaringizni kiriting.

Hayvonlar, o'simliklar, evolyutsiya, hayot daraxti, ekologiya, hujayralar, genetika, biologiya sohalari va boshqalar haqida bilib oling.

Muvaffaqiyat! Siz ko'rsatgan elektron pochta manziliga tasdiqlovchi xat yuborildi. 6 haftalik kursimizni boshlash uchun elektron pochtangizni tekshiring va havolani bosganingizga ishonch hosil qiling.

Asosiy biologiya: kirish

Bundan tashqari, Amazon, Kitob depozitariysi va boshqa barcha yaxshi kitob do'konlarida mavjud.


Biologlar gulli o'simliklarda uzoq umr ko'rish genini aniqlaydilar

Chapda: yovvoyi turdagi Arabidopsis thaliana. O'ngda: Arabidopsis thaliana haddan tashqari ifodalangan AHL15 bilan. Tasvir krediti: Omid Karami.

"O'simliklarning poyasida o'sish nuqtalari bor. Bu barglar yoki gullar bilan yangi poyalar hosil qila oladigan ildiz hujayralari guruhlari ”, - dedi Leyden universiteti Leyden biologiya instituti professori Remko Offringa va uning hamkasblari.

"Ko'p yillik o'simliklarda o'sadigan ko'plab joylar vegetativ bo'lib qoladi, shuning uchun gullashdan keyin o'simlik keyingi mavsumda o'sishda davom etishi mumkin. Bir yillik o'simliklarda bu sodir bo'lmaydi va o'simlik o'ladi.

"Biz o'simlikning o'sish nuqtalari gullashdan keyin vegetativ bo'lib qolishini aniqlaydigan genni topdik."

Tadqiqot uchun professor Offringa va hammualliflardan foydalanilgan Arabidopsis thaliana, Evropada, Osiyoda va Afrikaning shimoliy qismlarida tez o'sadigan gulli o'simlik.

"Biz AHL15 genini haddan tashqari oshirib yubordik Arabidopsis shuning uchun u odatdagidan ancha faolroq », - deb tushuntirishdi ular.

"Ko'p yillik o'simliklar singari, o'zgartirilgan Arabidopsis o'simliklar ba'zi o'sish nuqtalari vegetativ fazada qoladi. "

"O'simliklar gullashdan keyin o'sishda davom etadi va bir necha marta gullashi mumkin."

Tadqiqotchilar AHL15 genini o'chirib qo'yishganda, ular o'simliklarning umri qisqaroq ekanligini payqashdi.

"Genning kashf qilinishi o'simliklarning hayoti tarixi va qarishi haqidagi fundamental bilimlarga yordam beradi", - deydi professor Offringa.

"Gen, shuningdek, evolyutsiya jarayonida nega ba'zi turlar bir yillik, boshqalari esa ko'p yillik bo'lib qolgan, degan savolga javob berishi mumkin."

“Koʻpgina oziq-ovqat ekinlari, masalan, sholi va bugʻdoy bir yillik oʻsimliklardir. Ba'zi ekinlarni vegetativ holda ushlab turish o'simliklarni yig'ib olgandan keyin o'sishda davom etishiga imkon beradi. Bu bir xil hosildan bir necha marta hosil olish va shu orqali har bir o‘simlikdan hosilni oshirish imkonini beradi”.

“Fermerlar tez -tez gullaydigan o'simliklar etishtirganda ham kamroq shudgor qilishlari kerak. Natijada, tuproq biomasi saqlanib qoladi, bu qishloq xo'jaligida barqaror ishlab chiqarishga mos keladi ”.

O. Karami va boshqalar. Qo'ltiq osti meristemasining pishib etishining bostiruvchisi gulli o'simliklarning uzoq umr ko'rishiga yordam beradi. Nat. O'simliklar, onlaynda 13-aprel, 2020-da chop etilgan doi: 10.1038/s41477-020-0637-z


Tarkibi

Angiospermdan olingan xususiyatlar Tartibga solish

Angiospermlar boshqa urug 'o'simliklaridan quyidagi jadvalda tasvirlangan bir qancha jihatlari bilan farq qiladi. Birgalikda olingan bu farqlovchi xususiyatlar angiospermlarni eng xilma-xil va ko'p sonli quruqlik o'simliklari va odamlar uchun eng tijorat jihatdan muhim guruhga aylantirdi. [a]

Angiospermlarning o'ziga xos xususiyatlari
Xususiyat Tavsif
Gullaydigan organlar Gullar, gullaydigan o'simliklarning ko'payish organlari, ularni boshqa urug 'o'simliklaridan ajratib turadigan eng ajoyib xususiyatdir. Gullar angiospermlarga ko'proq turlarga xos naslchilik tizimiga ega bo'lish vositalarini taqdim etdi va shuning uchun tegishli turlar bilan kesishish xavfisiz har xil turlarga tezroq evolyutsiya qilish yo'li. Tezroq spetsifikatsiya Angiospermlarga kengroq ekologik bo'shliqlarga moslashishga imkon berdi. Bu gulli o'simliklarning quruqlik ekotizimlarida ustunlik qilishiga imkon berdi. [ iqtibos kerak ]
Ikki juft polen qopchasi bo'lgan stamens Stamenlar mos keladigan gimnosperm organlariga qaraganda ancha yengilroq va ma'lum changlatuvchilar kabi maxsus changlatish sindromlariga moslashib, angiospermlarning vaqt o'tishi bilan diversifikatsiyasiga hissa qo'shgan. Stamens, shuningdek, o'z-o'zini urug'lantirishning oldini olish uchun vaqt o'tishi bilan o'zgartirildi, bu esa keyingi diversifikatsiyaga imkon berdi va angiospermlarga oxir-oqibat ko'proq bo'shliqlarni to'ldirishga imkon berdi.
Erkak gametofit, uchta hujayradan kamaygan Angiospermalardagi erkak gametofitlari gimnosperm urug'li o'simliklarnikiga qaraganda ancha kamayadi. [10] Polenning kichik o'lchami changlanish - gulchang donasi urg'ochi o'simlikka etib borishi va urug'lantirish o'rtasidagi vaqtni qisqartiradi. Gimnospermlarda urug'lanish changlanishdan bir yil o'tgach sodir bo'lishi mumkin, angiospermlarda esa urug'lantirish changlatishdan keyin tez orada boshlanadi. [11] Changlatish va urug'lantirish o'rtasidagi qisqa vaqt angiospermlarga changlanishdan keyin gimnospermlarga qaraganda erta urug 'hosil qilish imkonini beradi, bu esa angiospermlarga aniq evolyutsion ustunlikni beradi.
Tuxumdonlarni o'rab turgan yopiq karpel (karpel yoki karpel va yordamchi qismlar mevaga aylanishi mumkin) Angiospermlarning yopiq karpeli, shuningdek, changlatishning maxsus sindromlari va nazoratiga moslashishga imkon beradi. Bu o'z-o'zidan urug'lanishni oldini olishga yordam beradi va shu bilan xilma-xillikni oshiradi. Tuxumdon urug'langach, karpel va uning atrofidagi ba'zi to'qimalar mevaga aylanadi. Bu meva ko'pincha urug'larni tarqatuvchi hayvonlar uchun jozibador bo'lib xizmat qiladi. Natijada paydo bo'lgan hamkorlik aloqasi tarqalish jarayonida angiospermlarga yana bir afzallik beradi.
Kamaytirilgan ayol gametofit, sakkiz yadroli etti hujayra Qisqartirilgan urg'ochi gametofit, erkak gametofitning kamayishi singari, tezroq urug 'yig'ish imkonini beradigan moslashuv bo'lishi mumkin, natijada har yillik otsu hayotiy davrlar kabi gullaydigan o'simliklarning moslashuviga olib keladi, bu esa gullaydigan o'simliklarga ko'proq joylarni to'ldirishga imkon beradi.
Endosperm Umuman olganda, endosperm shakllanishi urug'lantirilgandan keyin va zigotaning birinchi bo'linishidan oldin boshlanadi. Endosperm juda to'yimli to'qima bo'lib, u birinchi marta paydo bo'lganida rivojlanayotgan embrion, kotiledonlar va ba'zan ko'chatlarni oziq-ovqat bilan ta'minlaydi.

Qon tomir anatomiyasini tahrirlash

Angiosperm poyalari o'ngda ko'rsatilganidek, etti qatlamdan iborat. Gulli o'simliklarda to'qimalarning hosil bo'lishining miqdori va murakkabligi gimnospermlarnikidan oshadi. Poyaning tomir to‘plamlari shunday joylashtirilganki, ksilema va floema konsentrik halqalarni hosil qiladi.

Ikki pallalilarda juda yosh poyadagi to‘plamlar ochiq halqa shaklida joylashgan bo‘lib, markaziy chuqurchani tashqi qobiqdan ajratib turadi. Ksilema va floemani ajratib turadigan har bir to'plamda kamistem deb nomlanuvchi meristem yoki faol shakllantiruvchi to'qima qatlami joylashgan. To'plamlar o'rtasida kambiy qatlami hosil bo'lganda (interfasikulyar kambiy) to'liq halqa hosil bo'ladi va qalinligining muntazam ravishda vaqti -vaqti bilan ortib borishi ksilema va tashqi tomondan floemaning rivojlanishi natijasida yuzaga keladi. Yumshoq floema eziladi, lekin qattiq yog'och saqlanib qoladi va daraxtsimon ko'p yillik o'simlikning poyasi va shoxlarining asosiy qismini hosil qiladi. Mavsum boshida va oxirida hosil bo'lgan elementlarning xarakteridagi farqlar tufayli yog'och ko'ndalang kesimda konsentrik halqalarga ajratiladi, har bir o'sish mavsumi uchun bittadan yillik halqalar deb ataladi.

Monokotiledonlar orasida to'plamlar yosh poyada ko'proq va er to'qimasi bo'ylab tarqalgan. Ularda kambiy yo'q va faqat bir marta hosil bo'lganda, novda diametri faqat alohida holatlarda ko'payadi.

Reproduktiv anatomiya tahrirlash

Angiospermlarning o'ziga xos xususiyati - bu gul. Gullar shakl va ishlab chiqishda ajoyib o'zgarishlarni ko'rsatadi va angiosperm turlari o'rtasidagi munosabatlarni o'rnatish uchun eng ishonchli tashqi xususiyatlarni beradi. Gulning vazifasi - tuxumdonning urug'lanishini va urug'li mevalarning rivojlanishini ta'minlash. [ iqtibos kerak ] Gulli apparat nihoyat novdada yoki barg oqsida paydo bo'lishi mumkin (bu erda petiole poyaga birikadi). [ iqtibos kerak ] Ba'zan, binafshalarda bo'lgani kabi, gul oddiy barg bargining qo'ltig'ida yakka o'zi paydo bo'ladi. Odatda, o'simlikning gulli qismi bargli yoki vegetativ qismidan keskin farq qiladi va gulzor deb ataladigan ozmi-ko'pmi ishlab chiqilgan filial tizimini hosil qiladi.

Gullar tomonidan ishlab chiqariladigan ikki xil jinsiy hujayralar mavjud. Polen donalariga bo'linadigan mikrosporalar "erkak" hujayralar bo'lib, stamenlarda (yoki mikrosporofillarda) tug'iladi. [ iqtibos kerak ] Tuxum hujayrasi (megagametogenez) bo'lish uchun bo'linadigan megasporlar deb ataladigan "ayol" hujayralar tuxumdonda joylashgan va karpel (yoki megasporofill) bilan o'ralgan.

Gul faqat majnuntolda bo'lgani kabi faqat shu qismlardan iborat bo'lishi mumkin, bu erda har bir gul faqat bir nechta stamens yoki ikkita karpeldan iborat. Odatda, boshqa tuzilmalar mavjud bo'lib, sporofillalarni himoya qilish va changlatuvchilar uchun jozibali konvert hosil qilish uchun xizmat qiladi. Bu atrofdagi tuzilmalarning alohida a'zolari sepals va gulbarglar (yoki gullardagi tepalar) deb nomlanadi. Magnoliya bu erda sepals va gulbarglar bir-biridan farq qilmaydi). Tashqi seriya (tepaliklar kubogi) odatda yashil va bargsimon bo'lib, gulning qolgan qismini, ayniqsa kurtakni himoya qiladi. Ichki qator (barglarning gulbarglari) odatda oq yoki yorqin rangga ega bo'lib, tuzilishi jihatidan ancha nozikdir. U hasharotlar yoki qushlarning changlatuvchilarini jalb qilish vazifasini bajaradi. O'ziga jalb qilish rang, hid va nektar orqali amalga oshiriladi, ular gulning ba'zi bir qismida ajralib chiqishi mumkin. Changlovchilarni jalb qiluvchi xususiyatlar odamlar orasida gullar va gulli o'simliklarning mashhurligini hisobga oladi. [ iqtibos kerak ]

Gullarning aksariyati mukammal yoki germafrodit (bir xil gul tuzilishida ham polen, ham tuxumdon hosil qiluvchi qismlarga ega) bo'lsa-da, gullaydigan o'simliklar o'z-o'zidan urug'lanishni kamaytirish yoki oldini olish uchun ko'plab morfologik va fiziologik mexanizmlarni ishlab chiqqan. Geteromorf gullar kalta kalta va uzun stamensga ega, yoki aksincha, shuning uchun hayvon changlatuvchilar changni pistilga (karpelning retseptiv qismi) osonlikcha o'tkaza olmaydi. Gomomorf gullar o'z-o'zidan va o'z-o'zidan bo'lmagan polen donalarini ajratish uchun o'z-o'zidan mos kelmaslik deb ataladigan biokimyoviy (fiziologik) mexanizmdan foydalanishi mumkin. Shu bilan bir qatorda, ikki xonali turlarda erkak va urg'ochi qismlar morfologik jihatdan ajralib turadi, turli xil individual gullarda rivojlanadi. [12]

Tasniflash tarixi Tahrirlash

Botanika atamasi "angiosperm", yunoncha so'zlardan anjeyon ("shisha, idish") va sperma ("urug 'urug'i"), 1690 yilda Pol Hermann tomonidan "Angiospermae" shaklida, o'simlik dunyosining asosiy bo'linmalaridan birining nomi sifatida ishlab chiqarilgan. Bunga kapsulalarga o'ralgan, uning gimnospermasidan ajralib turadigan urug'li gulli o'simliklar yoki ochenal yoki shizo-karpali mevali gulli o'simliklar kiradi, bu erda butun meva yoki uning har bir bo'lagi urug 'va yalang'och hisoblanadi. Bu atama ham, uning antonimi ham Karl Linney tomonidan bir xil ma'noda, ammo cheklangan qo'llanilishi bilan o'z sinfining Didinamiya ordenlari nomlarida saqlanib qolgan. Uning zamonaviy doirasiga har qanday yondashuv bilan foydalanish faqat 1827 yildan keyin, Robert Braun sikadalar va ignabargli daraxtlarda chindan ham yalang'och tuxumdonlarning mavjudligini aniqlab, ularga Gymnosperms nomini qo'llaganidan keyin mumkin bo'ldi. [ iqtibos kerak ] O'sha paytdan boshlab, bu gimnospermlar odatdagidek, ikki pallali gulli o'simliklar deb hisoblanar ekan, Angiosperm atamasi botanik yozuvchilar tomonidan bir-biriga zid ravishda, har xil ko'lamli, boshqa ikki pallali o'simliklarning guruh nomi sifatida ishlatilgan.

1851 yilda Xofmayster gulli o'simliklarning embrion xaltasida sodir bo'ladigan o'zgarishlarni aniqladi va ularning kriptogamiyaga to'g'ri munosabatlarini aniqladi. Bu gimnospermlarning ikki pallali sinflardan farqli o'laroq o'rnini belgilab qo'ydi va keyinchalik angiosperm atamasi asta -sekin gimnospermlardan boshqa barcha gulli o'simliklar uchun mos belgi sifatida qabul qilindi. Bu atama bugungi kunda qo'llanilgan ma'nodir.

Aksariyat taksonomiyalarda gulli o'simliklar izchil guruh sifatida qaraladi. Eng mashhur tavsiflovchi ism Angiospermae bo'lib, Anthophyta ("gulli o'simliklar") ikkinchi tanlovdir (ikkalasi ham tartiblanmagan). Vettshteyn tizimi va Engler tizimi ularga bo'linma (Angiospermae) sifatida qaragan. Reveal tizimi ularni bir bo'linma (Magnoliophytina) sifatida ham ko'rib chiqdi [14], lekin keyinchalik uni Magnoliopsida, Liliopsida va Rosopsida ga ajratdi. Taxtajan tizimi va Cronquist tizimi ularga bo'linish (Magnoliophyta) sifatida qaraydi. Dahlgren tizimi va Torn tizimi (1992) ularni sinf (Magnoliopsida) sifatida ko'rib chiqadi. 1998 yildagi APG tizimi va 2003 yilgi [15] va 2009 yilgi [16] tuzatishlar gulli o'simliklarni rasmiy lotin nomisiz (angiospermlar) tartibsiz qatlam sifatida ko'rib chiqadi. Rasmiy tasnif 2009 yilgi reviziya bilan birga nashr etilgan bo'lib, unda gulli o'simliklar kichik sinf (Magnoliidae) deb hisoblanadi. [17]

Ushbu guruhning ichki tasnifi sezilarli darajada qayta ko'rib chiqildi. 1968 yilda Artur Kronquist tomonidan taklif qilingan va 1981 yilda to'liq shaklda nashr etilgan Cronquist tizimi hanuzgacha keng qo'llanilmoqda, lekin endi filogeniyani aniq aks ettirmaydi deb ishoniladi. Yaqinda 1998 yilda angiospermlarning ta'sirchan qayta tasnifini nashr etgan Angiosperm Filogenez Guruhi (APG) ishi natijasida gulli o'simliklarni qanday tartibga solish kerakligi haqida yakdillik paydo bo'la boshladi. So'nggi tadqiqotlarni o'z ichiga olgan yangilanishlar APG II tizimi sifatida nashr etildi. 2003 yilda, [15] 2009 yilda APG III tizimi, [16] [18] va 2016 yilda APG IV tizimi.

An'anaga ko'ra, gullaydigan o'simliklar ikki guruhga bo'linadi:

Cronquist tizimi Magnoliopsida ("Magnoliaceae" va Liliopsida ("Liliaceae" dan)) sinflarini tasniflaydi. ICBNning 16 -moddasida ruxsat berilgan boshqa tavsiflovchi ismlarga Dikotiledonlar yoki Dikotildonlar, Monokotiledonlar yoki Monokotiledonalar kiradi. Oddiy ingliz tilida ularning a'zolarini "ikki pallali" ("ikki nuqta") va "bir pallali" ("monokot") deb atash mumkin. Lotin bu nomlar ortida, odatda, dikotlarda ikkita kotiledon yoki embrion barglari borligini kuzatadi. Har bir urug '. Monokotlarning odatda bittasi bor, lekin qoida mutlaqo emas. Keng diagnostik nuqtai nazardan, kotiledonlarning soni unchalik qulay va ishonchli emas. [ iqtibos kerak ]

APG singari so'nggi tadqiqotlar shuni ko'rsatadiki, monokotlar monofil guruhini (klad) tashkil qiladi, lekin dikotlar parafiletikdir. Shunga qaramay, dikot turlarining aksariyati bir bo'lakka, eudikotlar yoki trikolpatlarga, qolganlarining aksariyati 9000 ga yaqin turni o'z ichiga oladigan magnoliidlarga kiradi. Qolganlari bazal angiospermlar deb nomlanuvchi erta shoxlangan taksonlarning parafiletik guruhini, shuningdek Ceratophyllaceae va Chloranthaceae oilalarini o'z ichiga oladi. [ iqtibos kerak ]

Zamonaviy tasniflash Tahrirlash

Tirik angiospermlarning sakkizta guruhi mavjud:

    (ANA: Amborella, Nymphaeales, Austrobaileyales)
    • Amborella, Yangi Kaledoniyadan kelgan bitta buta turi, 80 ga yaqin turi, [19] suv nilufar va Hydatellaceae, dunyoning turli burchaklaridan o'tinli o'simliklarning 100 ga yaqin turi [19].
      , 77 ta maʼlum [20] tishli barglari boʻlgan xushboʻy oʻsimliklarning 9000 ga yaqin turi, [19] uchburchak gullari, bir teshikli gulchanglari va odatda shoxlangan tomirli barglari bilan ajralib turadi—masalan, magnoliya, dafna dafna va qora qalampir, taxminan. 70 000 tur, [19] uchburchak gullar, bitta kotiledon, bir teshikli gulchanglar va odatda parallel tomirli barglari bilan ajralib turadi, masalan, o'tlar, orkide va palmalar.
    • Ceratophyllum, taxminan 6 turdagi suv o'simliklari [19], ehtimol akvarium o'simliklari bilan tanish bo'lgan, taxminan 175000 tur, [19] 4- yoki 5-gulli gullar, uch gözenekli polen va odatda shoxli tomirli barglari-masalan, kungaboqar. , petunya, sariyog ', olma va eman.

    Bu sakkiz guruh o'rtasidagi aniq munosabatlar hali aniq emas, garchi kelishuv mavjud bo'lsa -da, ajdodlar angiospermidan ajralib chiqqan birinchi uchta guruh Amborellales, Nymphaeales va Austrobaileyales (bazal angiospermlar) edi [21] Qolgan beshta guruhdan (yadro angiospermlari). , uchta eng keng guruh o'rtasidagi munosabatlar noaniq bo'lib qolmoqda (magnoliidlar, monokotlar va eudikotlar). Zeng va uning hamkasblari (1-rasm) to'rtta raqobatlashuvchi sxemani tasvirlaydi. [22] Eudikotlar va monokotlar eng katta va xilma -xil, bilan

    Angiosperm turlarining navbati bilan 75% va 20%. Ba'zi tahlillar magnoliidlarni birinchi bo'lib ajralib chiqadi, boshqalari esa monokotlardir. [23] Ceratophyllum monokotlar bilan emas, balki eudikotlar bilan guruhlanganga o'xshaydi. APG IV APG III da tasvirlangan umumiy yuqori tartibli munosabatlarni saqlab qoldi. [16]

    Nymphaeales Solsberi von Berchtold va Presl 1820 yil

    Magnoliales de Jussieu sobiq fon Berchtold va Presl 1820

    Laurales de Jussieu von Berchtold va Presl 1820 yil

    Alismatales Braun sobiq fon Berchtold va Presl 1820

    Pandanales Braun sobiq fon Berchtold & amp; Presl 1820

    Komelinallar de Mirbel ex von Berchtold va Presl 1820 yil

    Ranunculales de Jussieu sobiq fon Berchtold va Presl 1820

    Proteallar de Jussieu sobiq fon Berchtold va Presl 1820

    Dilleniales de Candolle sobiq fon Berchtold va Presl 1820

    Vitales de Jussieu von Berchtold va Presl 1820 yil

    Malpighiales de Jussieu von Berchtold va Presl 1820 yil

    Cucurbitales de Jussieu von Berchtold va Presl 1820 yil

    Geraniales de Jussieu von Berchtold va Presl 1820 yil

    Myrtales de Jussieu sobiq fon Berchtold va Presl 1820

    Sapindales de Jussieu sobiq fon Berchtold va Presl 1820

    Malvales de Jussieu von Berchtold va Presl 1820 yil

    Santalales Braun sobiq fon Berchtold & amp; Presl 1820

    Gentianales de Jussieu von Berchtold va Presl 1820 yil

    Solanales de Jussieu von Berchtold va Presl 1820 yil

    Boraginallar de Jussieu von Berchtold va Presl 1820 yil

    Dipsacales de Jussieu von Berchtold va Presl 1820 yil

    Evolyutsiya tarixi tahrirlash

    Paleozoy tuzatish

    Fosillashgan sporalar quruqlikdagi o'simliklar (embriofitlar) kamida 475 million yil davomida mavjud bo'lganligini ko'rsatadi. [24] Erta er usti o'simliklari, ular paydo bo'lgan yashil suv o'tlari singari, suzuvchi sperma bilan jinsiy yo'l bilan ko'paygan. [ iqtibos kerak ] Yerga moslashish yangi yashash joylariga sporlar tomonidan tarqalishi uchun tik meiosporangiyalarning rivojlanishi edi. [ iqtibos kerak ] Bu xususiyat ularning eng yaqin suv o'tlari qarindoshlari charophycean yashil suvo'tlarining avlodlarida etishmaydi. Keyinchalik er usti moslashuvi qon tomir sporofit to'qimalarida nozik, avaskulyar jinsiy bosqich - gametofitning saqlanishi bilan sodir bo'ldi. [ iqtibos kerak ] Bu urug'siz o'simliklarda bo'lgani kabi spora emas, balki sporangiya ichida spora o'sishi natijasida sodir bo'lgan. Bu qanday sodir bo'lishi mumkin bo'lgan hozirgi misolni erta rivojlangan sporaning rivojlanishida ko'rish mumkin Selaginella, boshoq moxi. Angiospermlarning ajdodlari uchun natija ularni qutiga, urug'ga o'rash edi.

    Ko'rinib turibdiki, deyarli zamonaviy gullarning qoldiqlari va juda xilma -xilligi, asta -sekin evolyutsiya nazariyasi uchun shunday muammo tug'dirganki, Charlz Darvin buni "jirkanch sir" deb atagan. [25] Biroq, qazilma qoldiqlari Darvin davridan beri ancha o'sdi va yaqinda angiosperm qoldiqlari topildi. Archaefructus, fotoalbom gimnospermlarning kashfiyotlari bilan bir qatorda, angiosperm xarakteristikalari bir necha bosqichda qanday qo'lga kiritilgan bo'lishi mumkinligini ko'rsatadi. [ iqtibos kerak ] Yo'qolib ketgan gimnospermlarning bir nechta guruhlari, xususan, urug 'ferns, gulli o'simliklarning ajdodlari sifatida taklif qilingan, lekin gullarning qanday paydo bo'lganligini ko'rsatadigan doimiy qazilma dalillar yo'q va botaniklar hali ham buni sir deb bilishadi. [26] Yuqori Trias kabi ba'zi qadimgi toshqotgan qoldiqlar Sanmigueliya levisi, taklif qilingan. [ iqtibos kerak ]

    Birinchi urug'li o'simliklar, ginkgo va ignabargli daraxtlar (qarag'ay va archa kabi) kabi, gul bermagan. Ning polen donalari (erkak gametofitlari) Ginkgo sikadlar esa rivojlanayotgan gulchang naychasi boʻylab urgʻochi va uning tuxumlarigacha “suzuvchi” bir juft bayroqchali, harakatchan sperma hujayralarini hosil qiladi.

    Ko'p gulli o'simliklar ishlab chiqaradigan ikkilamchi metabolit Oleanan o'sha davrdagi Perm yotqiziqlarida gigantopteridlarning qoldiqlari bilan birga topilgan. [27] [28] Gigantopteridlar yoʻq boʻlib ketgan urugʻli oʻsimliklar guruhi boʻlib, ular gulli oʻsimliklar bilan koʻp morfologik belgilarga ega, ammo ularning oʻzlari gulli oʻsimliklar ekanligi maʼlum emas. [ iqtibos kerak ]

    Trias va yura tuzatishlari

    Mavjud dalillarga asoslanib, ba'zilar angiospermlarning ajdodlari trias davrida (245-202 million yil oldin) noma'lum gimnospermlar guruhidan ajralib chiqqanligini taxmin qilmoqdalar. Fossil angiosperm-like pollen from the Middle Triassic (247.2–242.0 Ma) suggests an older date for their origin. [29] A close relationship between angiosperms and gnetophytes, proposed on the basis of morphological evidence, has more recently been disputed on the basis of molecular evidence that suggest gnetophytes are instead more closely related to other gymnosperms. [30] [31]

    The fossil plant species Nanjinganthus dendrostyla from Early Jurassic China seems to share many exclusively angiosperm features, such as a thickened receptacle with ovules, and thus might represent a crown-group or a stem-group angiosperm. [32] However, these have been disputed by other researchers, who contend that the structures are misinterpreted decomposed conifer cones. [33] [34]

    The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. [35] These occurred at 319 million years ago and 192 million years ago . Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. [36] That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda, [37] and directly addresses Darwin's "abominable mystery".

    One study has suggested that the early-middle Jurassic plant Schmeissneria, traditionally considered a type of ginkgo, may be the earliest known angiosperm, or at least a close relative. [38]

    Cretaceous Edit

    Whereas the earth had previously been dominated by ferns and conifers, angiosperms appeared and quickly spread during the Cretaceous. They now comprise about 90% of all plant species including most food crops. [39] It has been proposed that the swift rise of angiosperms to dominance was facilitated by a reduction in their genome size. During the early Cretaceous period, only angiosperms underwent rapid genome downsizing, while genome sizes of ferns and gymnosperms remained unchanged. Smaller genomes—and smaller nuclei—allow for faster rates of cell division and smaller cells. Thus, species with smaller genomes can pack more, smaller cells—in particular veins and stomata [ iqtibos kerak ] —into a given leaf volume. Genome downsizing therefore facilitated higher rates of leaf gas exchange (transpiration and photosynthesis) and faster rates of growth. This would have countered some of the negative physiological effects of genome duplications, facilitated increased uptake of carbon dioxide despite concurrent declines in atmospheric CO2 concentrations, and allowed the flowering plants to outcompete other land plants. [40]

    The oldest known fossils definitively attributable to angiosperms are reticulated monosulcate pollen from the late Valanginian (Early or Lower Cretaceous - 140 to 133 million years ago) of Italy and Israel, likely representative of the basal angiosperm grade. [33]

    The earliest known macrofossil confidently identified as an angiosperm, Archaefructus liaoningensis, is dated to about 125 million years BP (the Cretaceous period), [41] whereas pollen considered to be of angiosperm origin takes the fossil record back to about 130 million years BP, [42] with Montsechia representing the earliest flower at that time. [43]

    In 2013 flowers encased in amber were found and dated 100 million years before present. The amber had frozen the act of sexual reproduction in the process of taking place. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects. [44] In August 2017, scientists presented a detailed description and 3D model image of what the first flower possibly looked like, and presented the hypothesis that it may have lived about 140 million years ago. [45] [46] A Bayesian analysis of 52 angiosperm taxa suggested that the crown group of angiosperms evolved between 178 million years ago and 198 million years ago . [47]

    Recent DNA analysis based on molecular systematics [48] [49] showed that Amborella trichopoda, found on the Pacific island of New Caledonia, belongs to a sister group of the other flowering plants, and morphological studies [50] suggest that it has features that may have been characteristic of the earliest flowering plants. The orders Amborellales, Nymphaeales, and Austrobaileyales diverged as separate lineages from the remaining angiosperm clade at a very early stage in flowering plant evolution. [51]

    The great angiosperm radiation, when a great diversity of angiosperms appears in the fossil record, occurred in the mid-Cretaceous (approximately 100 million years ago). However, a study in 2007 [52] estimated that the division of the five most recent of the eight main groups occurred around 140 million years ago. (the genus Ceratophyllum, the family Chloranthaceae, the eudicots, the magnoliids, and the monocots) .

    It is generally assumed that the function of flowers, from the start, was to involve mobile animals in their reproduction processes. That is, pollen can be scattered even if the flower is not brightly colored or oddly shaped in a way that attracts animals however, by expending the energy required to create such traits, angiosperms can enlist the aid of animals and, thus, reproduce more efficiently.

    Island genetics provides one proposed explanation for the sudden, fully developed appearance of flowering plants. Island genetics is believed to be a common source of speciation in general, especially when it comes to radical adaptations that seem to have required inferior transitional forms. Flowering plants may have evolved in an isolated setting like an island or island chain, where the plants bearing them were able to develop a highly specialised relationship with some specific animal (a wasp, for example). Such a relationship, with a hypothetical wasp carrying pollen from one plant to another much the way fig wasps do today, could result in the development of a high degree of specialisation in both the plant(s) and their partners. Note that the wasp example is not incidental bees, which, it is postulated, evolved specifically due to mutualistic plant relationships, are descended from wasps. [53]

    Animals are also involved in the distribution of seeds. Fruit, which is formed by the enlargement of flower parts, is frequently a seed-dispersal tool that attracts animals to eat or otherwise disturb it, incidentally scattering the seeds it contains (see frugivory). Although many such mutualistic relationships remain too fragile to survive competition and to spread widely, flowering proved to be an unusually effective means of reproduction, spreading (whatever its origin) to become the dominant form of land plant life. [ iqtibos kerak ]

    Flower ontogeny uses a combination of genes normally responsible for forming new shoots. [54] The most primitive flowers probably had a variable number of flower parts, often separate from (but in contact with) each other. The flowers tended to grow in a spiral pattern, to be bisexual (in plants, this means both male and female parts on the same flower), and to be dominated by the ovary (female part). As flowers evolved, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant or at least "ovary-inferior". Flower evolution continues to the present day modern flowers have been so profoundly influenced by humans that some of them cannot be pollinated in nature. Many modern domesticated flower species were formerly simple weeds, which sprouted only when the ground was disturbed. Some of them tended to grow with human crops, perhaps already having symbiotic companion plant relationships with them, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection. [55]

    A few paleontologists have also proposed that flowering plants, or angiosperms, might have evolved due to interactions with dinosaurs. One of the idea's strongest proponents is Robert T. Bakker. He proposes that herbivorous dinosaurs, with their eating habits, provided a selective pressure on plants, for which adaptations either succeeded in deterring or coping with predation by herbivores. [56]

    By the late Cretaceous, angiosperms appear to have dominated environments formerly occupied by ferns and cycadophytes, but large canopy-forming trees replaced conifers as the dominant trees only close to the end of the Cretaceous 66 million years ago or even later, at the beginning of the Paleogene. [57] The radiation of herbaceous angiosperms occurred much later. [58] Yet, many fossil plants recognisable as belonging to modern families (including beech, oak, maple, and magnolia) had already appeared by the late Cretaceous. Flowering plants appeared in Australia about 126 million years ago. This also pushed the age of ancient Australian vertebrates, in what was then a south polar continent, to 126-110 million years old. [43]


    [PDF] Anatomy of Flowering Plants NEET Biology Study Material

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    ANGIOSPERMS (FLOWERING PLANTS)

    Angiosperms are most dominant and most evolved plants on this earth, appeared about 130 million years ago in Jurassic (dicot plant) and cretaceous (monocot plants) period of the Mesozoic era. Tertiary period of Cenozoic era is called as Age of angiosperms.

    Angiosperms are found in every habitat. They constitute more than 50% of the total plants on this earth.

    Angiosperms are seed bearing, flowering vascular plants in which seeds are enclosed in fruits. The term angiosperm means ‘enclosed seeds’ as seeds (ovules) are found enclosed in the ovary wall.

    Instead of a cone, angiosperms bear flowers. The flower is the most characteristic structure of the angiosperms.

    The flower is defined as a modified shoot meant essentially for the reproduction of the plant.

    The flower usually develops as a branch from a bud, growing in the axil of a small leaflike structure known as bract. A stalk called pedicel supports the flower in the axil of the bract. The upper swollen end of the pedicel called receptacle or thalamus bears all the floral parts.

    A typical angiospermic flower consists of 4 whorls, viz., calyx, corolla, androecium and gynoecium. Both calyx and corolla are known as accessory or helping whorls. The androecium and gynoecium are called reproductive or essential whorls.

    Androecium (stamen) is microsporophyll and gynoecium (carpel) is megasporophyll. Megasporophyll is differentiated into ovary, style and stigma.

    Angiosperms lack both archegonia and antheridia. The archegonium is replaced by gynoecium (pistil) and antheridium by pollen tube.

    Flowers are adapted for various modes of pollination by birds, air, water, insects, etc.

    The outermost axillary whorl of the flower is the calyx, represented by the sepals.

    Corolla is the second whorl of flower present inner to calyx and is composed of petals. The bright color of the petals combined with the scent of essential oils present in some flowers makes the flower highly attractive to insects which act as agents for pollination.

    The angiosperms are an exceptionally large group of plants occurring in wide range of habitats. They range in size from tiny, almost microscopic Wolffi too tall trees of Eucalyptus (over 100 metres). They provide food, fodder, fuel, medicines and several other commercially important products.

    The male sex organs in a flower is the stamen. Each stamen consists of a slender filament with an anther at the tip. The anthers after meiosis, produce pollen grains.

    The female sex organs in a flower are the pistil or the carpel. Pistil consists of an ovary enclosing one to many ovules. Within ovules are present highly reduced female gametophytes termed embryosacs. The embryo-sac formation is preceded by meiosis. Hence, each of the cells of an embryo-sac is haploid. Each embryo-sac has a three-celled egg apparatus – one egg cell and two synergids, three antipodal cells and two polar nuclei. The polar nuclei eventually fuse to produce a diploid secondary nucleus.

    Pollen grain shed at 2-3 celled stage after dispersal from the anthers is carried by wind or various other agencies to the stigma of a pistil. This is termed as pollination.

    The pollen grains germinate on the stigma and the resulting pollen tubes grow through the tissues of stigma and style and reach the ovule.

    The pollen tubes enter the embryo-sac where two male gametes are discharged.

    One of the male gametes fuses with the egg cell to form a zygote (syngamy).

    The other male gamete fuses with the diploid secondary nucleus to produce the triploid primary endosperm nucleus (PEN) known as triple fusion.

    Because of the involvement of two fusions, this event is termed as double fertilisation, and event unique to angiosperms.

    The zygote develops into an embryo (with one or two cotyledons) and the PEN develops into endosperm which provides nourishment to the developing embryo.

    The synergids and antipodals degenerate after fertilisation.

    During these events, the ovules develop into seeds and the ovaries develop into a fruit.

    A fruit is a ripened ovary. The ovary wall enlarges due to cell division and cell enlargement and is termed the pericarp. In fl eshy fruits, the pericarp is often differentiated into epicarp,
    mesocarp and endocarp.

    A true fruit is one which develops directly from an ovary. Sometimes other parts of the flower such as thalamus, sepals, etc. become a part of the fruit. Such fruits are termed false, spurious or pseudocarp, as in cashew-nut, apple, strawberry, etc.

    Ular ikki sinfga bo'lingan:

    the dicotyledons and the monocotyledons.

    The dicotyledons are characterised by having two cotyledons in their seeds while the monocotyledons have only one.


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