Page 22 - Pharmacognosy-I (02-06-06-102)

Introduction

Definition: A seed is the mature fertilized ovule. It contains an embryo and
is constructed to insure the continuation and distribution as well as the
transportation of the plant.
Structure of the ovule
A typical mature ovule consists of:
1- The Nucellus:

A mass of parenchmatous tissue including a large cell called the embryo
sac.
2- The integuments:
The ovule shows one or two integuments enveloping the nucellus with
exception of a narrow opening called the micropyle for the entry of the
pollen tube of the pollen grain.
3- The embryo sac:
It is a large cell having eight or seven nuclei

4- Chalaza The basal part of the nucellus, from which arise the integuments
is somewhat swollen and called chalaza.

The ovule may be sessile or commonly attached at the chalaza to the
placenta by a small stalk called funicle, which may fuse for some distance
with the integument to form the raphe.

The ovule

structure

Type of ovules
The mature ovule exhibits several types:

A- Atropous or orthotropous : When growth is uniform, the ovule is
straight, not curved, having funicle, chalaza and micropyle on one straight

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