STRUCTURE & TYPES OF OVULES

INDIA BIOLOGY- NEET September 02, 2020 0

STD-12 UNIT-6 CHA-2

REPRODUCTION IN FLOWERING PLANT

STRUCTURE & TYPES OF OVULES

STRUCTURE OF OVULE

Ovule is an integumented megasporangium found in sper matophytes which develops into seed after fertilisation .
An angiospermic ovule is typically an ovoid and whitish structure .
It occurs inside ovary where it is attached to a parenchy matous cushion called placenta either singly or in a cluster .
The ovule is stalked . The stalk is called funiculus or funicle .
The point of attachment of the body of the ovule with the funiculus is known as hilum .
Depending upon the configuration and orientation of the body of ovule in relation to funiculus ,

TYPES OF OVULES

In the typical ( anatropous ) ovule the funiculus is fused with body of the ovule lengthwise beyond the hilum .
It gives rise to a longitudinal ridge called rapbe .
Funicu lus contains a vascular strand for the supply of nourishment to the ovule .
The body of the ovule consists of a mass of parenchymatous cells named nucellus .
It is equivalent to megasporangium .
Nucellus may be quite massive ( crassinucellate ovule ) or thin ( tenuinucellate ovule ) .
It is surrounded by one ( unitegmic ovule , e.g. , higher dicots ) or two ( bitegmic ovule , e.g. , monocots and primitive dicots ) multicellular integuments .
Rarely an ovule may be surrounded by three integuments ( tritegmic , e.g .Asphodelus ) or the integuments are absent ( ategmic , e.g. , Santalum ) .
Free surfaces of nucellus and integuments are covered by cuticle .
The integuments leave a narrow pore or passage at one end of theovule .
It is known as micropyle .
The place of origin of the integuments usually lies at the opposite end, It is termed as chalaza .
Female gametophyte or embryo sac is embedded in the micropylar half of the nucellus .

Gene Therapy and Its types