Question

How ovule is attached to placenta by a stalk called?

Answer 1

(a) The ovule (megasporangium):

The placenta a ridge of tissue a parenchymatous mass in the inner wall of the ovary to which ovules are attached. The manner in which the placentae are distributed in the cavity of an ovary is called placentation.

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Each ovule is attached to the placenta by a slender stalk called funicle. The point of attachment of the body of the ovule to its stalk or funicle is known as hilum. The inverted ovule, the part of funicle remain attached beyond the hilum alongside of the body of the ovule forming a sort of ridge called raphe (Fig. 2.11).



The ovule contains a mass of thin walled parenchymatous cells called nucellus. The nucellus is protected by one or two multicellular coats called integuments. The basal portion of the nucellus from where the integuments appear is called chalaza.

In gymnosperms, family Compositae and few other families with gamopetalous corolla, there is one integument. The ovules with one integument are called unitegmic and with two integuments are known as bitegmic. A small opening is left at the apex of integuments known as micropyle.

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Female gametophyte or embryo sac is embedded in the micropylar region of nucellus. Depending upon the thickness of the nucellus, ovules are called tenuinucellate (nucellus thin) and crassinucellate (nucellus massive).

Different types of ovules have been reported in angiosperms on the basis of relationship of funicle with body of the ovule and orientation of the latter (e.g. orthotropous—upright or erect ovule and variously curved like anatropous, campylotropous, amphitropous and circinotropous)