Structure of ovule

Structure of ovule

1. Structure of Ovule & Types of ovule Dr. Vasanta I. Kahalkar Assistant Professor Department of Botany M. G. Arts, Science & Late N. P. Commerce College Armori

2. Ovule is the fertile part of Pistil. Morphologically it is called megasporangium . The ovule consists of the stalk and the body. It is protective outer coat are called integuments and the stalk called funicle . The ovule may have either one or two integuments. Ovule with one integuments are called unitegmic ovules and those have with two integument are bitegmic . The integuments envelops the inner nucellus except at one place which is the opening known as micropyle . This micropyle is the main passage area for the entry of pollen tube. Nucellus is the fertile part that form the female gametophyte (embryo sac). Basal region of the ovule is called chalaza . Structure of ovule

3. Following are the conditions seen in ovule in relation to integuments : ( i ) Unitegmic : Ovule with a single integument, e.g., sympetalous or gamopetalous dicotyledons . (ii) Bitegmic : Ovule with two integuments as in polypetalous ( Archichlamydeae ) dicotyledons and monocotyledons. (iii) Caruncle : It is formed as an outgrowth of the outer integument in the micropylar region. Caruncle is common in the ovules of Euphorbiaceae . e.g., Castor ( Ricinus ). (iv) Aril : In Asphodelus , a 3 rd integuments called aril. Arises from the base of ovule & its covers complete the other two integument. (v) Ategmic : In some parasites like Loranthus , Viscum , Santalum etc., there is no integument. Such an ovule is called ategmic .

4. Types of Ovules Based on the position of micropyle and chalaza with respect to funicle , the ovule are of following six types. a) Orthotropous b) Anatropous c) Hemi-anatropous d) Campylotropous e) Amphitropous f) Circinotropous

5. Orthotropous The micropyle , chalaza and funicle are in straight line. This is most primitive type of ovules. e.g., Betel, Piper, Polygonum .

6. 2. Anatropous The body of the ovule is completely inverted (turn at 180o angle ) so that micropyle and funicle come to lie very close to each other. e.g., 82% of angiosperm families.

7. 3. Hemi-anatropous Ovule turns at 90 angle upon the funicle or body of ovule is at right angle to the funicle e.g., Ranunculus.

8. 4. Campylotropous Ovule is circled more or less at right angle to funicle . Micropylar end is bent down slightly. e.g., in members of Leguminosae and Cruciferae .

9. 5. Amphitropous The body of the ovule is very much curved and embryo sac becomes curved like horse shoe e.g. Lemna , Poppy ,

10. 6 Circinotropous The funicle in this case is especially long that it creates a nearly full circle around the ovule and micropyle is ultimately pointing upwards.

11. Circinotropous Campylotropous Orthotropous Hemi-anatropous Anatropous

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