ffiXOTHEHA MUT. LATA AND (E. MUT. SEMILATA. 539 
tlie lata, and semilata forms, tiie 15 chromosomes are 
usually distributed so that 7 go to one daughter-nucleus and 
8 to the other. In rare cases the distribution is 9 and 6. 
Only four such cases were observed, in one of which one 
chromosome also divided, making the distribution 9J + 5-J. 
More frequently the extra chromosome is left behind, where 
it may be seen fragmenting and degenerating in the cyto- 
plasm. In such cases the four pollen grains formed from a 
mother-cell will each contain 7 chromosomes. Hence while 
theoretically equal numbers of germ-cells having 7 and 8 
chromosomes would be anticipated, actually the number 
having 8 is a much smaller proportion. 
A still more interesting fact with regard to the cytological 
behaviour in these plants is that one chromosome, which is 
probably the extra chromosome, not infrequently divides 
longitudinally in the heterotypic mitosis, its two halves passing 
to the daughter-nuclei. That is, unlike the other chromo- 
somes, this one divides in the first instead of the second 
reduction division. 
The later history of these half-chromosomes is of much 
interest. We have observed no case in which they pass 
undivided to one pole of the homotypic spindle. In normal 
homotypic anaphases we have invariably found the chromo- 
somes all dividing regularly and their halves passing to the 
poles. But we have observed homotypic metaphase groups 
(cf. fig. 24) containing each an apparently normal half- 
chromosome, and in such cases we believe that the half- 
cbromosome will either degenerate or, as a rare occurrence, 
pass undivided into one of the tetrad nuclei, thus producing a 
pollen grain with 8 chromosomes. There is no reason for 
supposing that such pollen grains would differ from those 
formed by the regular division of 8 whole chromosomes on the 
homotypic spindle. In any case, it is highly improbable that a 
chromosome which has undergone fission in the heterotypic 
mitosis will divide again in the homotypic, unless merely as a 
fragmentation accompanied by degeneration ; and hence for 
such chromosomes the second will be the reducing division. 
