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A Handbook of Biology

SPØRØPHÝLLS ÅRË ØF 2 TÝPËS:

Microsporophylls:

They

are

arranged

to

form

male

strobili

(microsporangiate). They bear microsporangia. The microspores develop

into male gametophytes. It is highly reduced and confined to only a limited

number of cells. This gametophyte is called a pollen grain. The pollen grains

are developed within the microsporangia.

Megasporophylls:

They

are

arranged

to

form

female

strobili

(macrosporangiate). They bear megasporangia (ovules).

The male or female cones may be borne on the same tree (Pinus) or on

different trees (Cycas).

The megaspore mother cell is differentiated from one of the cells of

nucellus. The nucellus is protected by envelops and the composite

structure is called an ovule.

Megaspore mother cell undergoes meiosis to form four megaspores.

One of the megaspores enclosed within the megasporangium (nucellus)

develops into a multicellular female gametophyte that bears two or more

archegonia.

The

multicellular

female

gametophyte

is

also

retained

within

megasporangium.

ÅÑGÏØSPËRMS



Angiosperms are flowering plants



Specialised reproductive structures are

flowers



Seeds are enclosed in fruits



Ovary – develops into fruit



Ovules – develop into seeds



Double

–

fertilisation

is

characteristic

feature of angiosperms. (AIPMT 2002)



Pollination occurs with the help of insects, birds, water or wind



Size range is from tiny, almost microscopic Wolfia to tall trees of

Eucalyptus (over 100 metres).



They provide us with food, fodder, fuel, medicines and several other

commercially important products.