82 
R. Ruggles Gates. 
chromosomes and two with only 6. The same irregularity has 
since been seen in various other types. There can be no reasonable 
doubt that lata originates in this way, through the union of a germ 
cell having 8 with one having 7 chromosomes, unless we deny some of 
the best established facts in cytology. Stomps, however (1916), 
goes so far as to deny the probability of this hypothesis, although 
he does not venture to offer anything in its place. His denial is 
based on the fact that several mutant types are known to have 15 
chromosomes. But, as has been pointed out, 1 if the 7 
gametophyte chromosomes are unlike, as is probable from many 
general cytological considerations, then 7 distinct types with 15 
chromosomes are to be anticipated. Up to the present, no such 
number of forms having 15 chromosomes has been described from 
any strain of CEnothera , nor have seven such forms been 
authenticated altogether, although there is no obvious reason why 
they should not ultimately be found. 
The evidence, then, is clear and definite that lata originated 
through a chromosome entering the wrong nucleus in the reduction 
division. In this way two pollen grains, or one megaspore will be 
produced, each having 8 chromosomes in its nucleus. The presence 
of the extra chromosome, as a duplicate of one, will no doubt 
immediately have its effect on the cytoplasm of the pollen grain or 
megaspore containing it. So that the mutation must quickly 
become a property of the cell as a whole, and, theoretically, at 
least, this will alter the character of the whole male or female 
gametophyte derived from a spore with 8 chromosomes, though the 
differences may not always be demonstrable by the microscope. 
Renner (1919) has shown that visible differences exist between the 
pollen grains and male gametophytes of various species, and that 
segregation of these characters takes place in the pollen of the Fj 
hybrids. If an egg from a mutated megaspore has 8 chromosomes, 
it is already different both in nucleus and cytoplasm from an 
ordinary egg of the type, since the extra chromosome has been 
producing its effect thoughout all stages of the embryo-sac formation. 
Nevertheless, the only original change which it is necessary to 
assume, to account for the appearance of lata , is a chance irregularity 
in which both members of a pair of chromosomes enter the same 
nucleus in the reduction division. To endeavour to explain the 
origin of CE. lata through an alteration in a hypothetical pangen 
when the visible facts of the chromosome structure are so clear, is to 
desert science for obscurantism. 
1 Gates, 1915, p. 181. 
