(EXOrilKliA MUT. LATA ANJ) CL. MUT. SLMILATA. 
545 
(K. Biennis mut. Bata. 
Tlie study of the pollen development in biennis lata 
showed conditions similar to those in lata riibricalyx, but 
tlie latter plant produced a good amount of viable pollen, 
while the former was quite sterile. The reasons for these 
differences in sterility are not apparent. 
Fig. 36 is a polar view of the heterotypic spindle in 
biennis lata, showing the 15 chromosomes. Figs. 38 and 
39 represent the usual condition in the homotypic metapliase, 
showing the 7-8 distribution of chromosomes. In fig. 38 
the spindles are at right-angles to each other, and all tlie 
chromosomes can be clearly counted. In fig. 39 the groups 
are seen in somewhat oblique view, so that a number of 
the chromosomes show the longitudinal split. Fig. 40 
portrays an exceptional case. The two metaphase groups 
on the homotypic spindles contain respectively and 8J 
chromosomes. Hence not only did one chromosome, probably 
the extra, split in the heterotypic division, but one other 
chromosome of the seven pairs also passed to the wrong pole 
of the spindle. This case is very clear, and admits of no 
other interpretation. 
Fig. 41 a and h represents a case of a 9-6 heterotypic 
distribution of the chromosomes in biennis lata, ddie two 
homotypic spindles were at right-angles in the cell. 
Another similar group of 9 chromosomes was found in this 
plant, a third in a typical lata (No. 179 .1.2), and in the 
lata-like plant, 229 . I . 10, one case of 9J + 5J chromosomes 
was found. 
Irregularities of this kind are occasional occurrences in 
all the 14-chromosome forms, and result in an 8-6 disti-i- 
bution of the chromosomes. There can be no doubt that 
to such irregularities are due the origin of all the lata 
and semilata series of mutants. These irregularities 
have been observed by one of us in HI. mut. rubrinervis 
1908a), lata x Lamarckiana (1910), and CE. biennis 
(Gates), and by Davis in CE . Lamarckiana (1911), and 
