Types of ovule: There are six types of ovules.
1. Orthotropous or atropous ovule (ortho-straight, tropous - turn)
The body of the ovule is erect or straight. The hilum, chalaza and the micropyle lie in a straight line e.g. Polygonum.
2. Anatropous ovule (ana - backward or up, tropous - turn)
The body of the ovule becomes completely inverted during the development so that the micropyle lies very close to the hilum (eg) Gamopetalae members.
3. Hemi-anatropous or hemitropous ovule
The body of the ovule is placed transversely at right angles to the funicle. The micropyle and chalaza lie in one straight line e.g.Ranunculus.
4. Campylotropous ovule (kampylos - curved)
The body of the ovule is curved or bent round so that the micropyle and chalaza do not lie in the same straight line. e.g.Leguminosae.
5. Amphitropous ovule
The curvature of the ovule is very much pronounced and the embryosac also becomes curved e.g. Allismaceae, and Butomaceae.
6. Circinotropous ovule
The nucellus and the axis are in the same line in the beginning but due to rapid growth on one side, the ovule becomes anatropous. The curvature continues further and the micropyle again points upwards (e.g.) Opuntia.