526 Cannon : Studies in Plant Hybrids : 



and Debarbieux. Their relatively large size and small number 

 make the observation of them comparatively easy and sure. The 

 reduced number is seven ; this number was repeatedly seen in the 

 first division and was verified in the second mitosis and in that of 

 the division of the nucleus of the tetrad also. 



The chromosomes in the anaphases of this division are more or 

 less bent and some show the splitting sometimes seen in these 

 stages of division. There was an equal apportionment of the 

 chromosomes, both as regards their number and size, to the 

 daughter nuclei. The single exception to this, and the only ab- 

 normality noticed in the hybrids, is shown in /. 2j. In the nu- 

 cleus from which the sketch was made one chromosome lagged 

 behind its companions ; fission, also, had not taken place. 



The daughter nuclei undergo reconstruction to a greater de- 

 gree than was observed in the cotton hybrid, but on account of 

 the small size of the nuclei the study of them is difficult and unsat- 

 isfactory. The chromosomes in early telophase are much elon- 

 gated and appear to unite end to end to form a single spireme, 

 which later becomes lumpy and more or less reticular. The 

 identity of the chromosomes is quite lost. 



In the prophases of the second division a spireme, which does 

 not seem to be split, may be seen, and the chromosomes formed 

 from it become associated in pairs in the nuclear plate, but they 

 may not on that account, as Mottier shows, be sister chromo- 

 somes. It is probable, however, that they are, and that they are 

 not homologous with the pairs found in the presynaptic division. 

 The metaphase or the anaphases present no noteworthy condition. 

 The reduced number of chromosomes, seven, was frequently ob- 

 served and the number verified. 



In late anaphases of the second division the cell-plates sepa- 

 rating the daughter nuclei may be seen, and when the grand- 

 daughter nuclei are reconstructed cell-division occurs. Immediately 

 after the division of the cell the tetrads are angular in form, but 

 they soon become spherical and at length they assume the ellip- 

 tical form characteristic of the pollen-grain. During these changes 

 in form the tetrad increases much in size and the nucleus of the 

 young spore moves from its early central position to one end of the 

 cell and there prepares for the division of the nucleus of the mi- 

 crospore. 



