Sept, 1921.] YASUI.— ON THE BEHAVIOR OF CHROMOSOMES 



159 



form a small pollen grain by itself, so that some pollen mother cells 

 contain some extra pollen grain or grains. 



Fig. 1. 



Fig. 1. The pollen mother cells, ■with voung pollen grains formed in it. a, four 

 pollen grains formed; b, a mother cell containing four pollen grains, one at center 

 with an isolated chromosome besides a normal nucleus, one to the left and one below, 

 containing no nuclei, under way of degeneration ; c, two grains contain each an extra 

 dwarf nucleus ; d, a mother cell containing four normal sized pollen grains and a 

 dwarf pollen grain ; e, a mother cell containing one abnormally large pollen grain 

 (diploid), two ordinary pollen grains and a dwarf pollen grain; f, a mother cell 

 having two unusually large (diploid) pollen grains. 



The division of the large nucleus, resulting from the fusion of 

 the two daughter nuclei, formed b\' the first division, very much 

 resembles an ordinary' somatic diyision ; and it results in the forma- 

 tion of two large daughter nuclei (PI. Ill, Fig. 23), each of which 

 has naturally an excessive number of chromosomes for a haploid 

 nucleus. Thus the large pollen grains, only two in number contained 

 in a mother cell, may be produced. (Text-fig. 1, f). 



In some specimen, two daughter nuclei of the first division, having 

 no partition wall between, are situated very near to each other ; 

 then the two spindles of the second division disturb each other, so 

 that there arise great irregularities. Likewise the two groups of 

 telophasic chromosomes derived from two different nuclei sometimes 



