Cytology ofCoccinia Indica W. & A. with reference to the behaviour of its sex-chromosomes

Summary

A study of the somatic mitosis ofCoccinia indica has shown that there are 24 chromosomes in the nuclei of both male and female plants, of which one pair is heteromorphic (XY) in the male and homomorphic (YY) in the female.

The somatic metaphase spindle originates from the polar caps which appear as a result of the shrinkage of the prophase nucleus.

During synizesis of the pollen mother cell the tapetal cells become binucleate. In certain cases the nuclear divisions are followed by cytokinesis. The two nuclei of the daughter cell again divide, and the later nuclear divisions may or may not be followed by wall formation.

At diakinesis of the pollen mother cell 12 bivalents have been seen, of which one is heteromorphic and has been found to be attached to the nucleolus.

A polar view of metaphase I shows 12 bivalents. One of these is decidedly bigger than the others and is the sex-chromosome pair (XY), whose identity could be followed during most of the later stages of meiosis.

Various forms of abnormalities have been noted, among which cytomixis and the binucleate condition of the pollen mother cells appear to be the most common.

Laggards have been found to be characteristic of the species. The lagging univalents organize micronuclei which subsequently divide along with the dyad nuclei, resulting in polyspory.