30 BOTANICAL GAZETTE [JULY 
tudinal halves of the daughter chromosomes of the heterotypic 
mitosis. Whether an approximation of threads or a split in a single 
thread occurs in synapsis was not determined with certainty from the 
observations, but various considerations lead to the belief that in 
Oenothera the doubling is due to a split which closes up later, rather 
than to an approximation of separate spirems. 
2. The conclusion that the method of reduction probably differs 
in different genera is based on two considerations: (1) the fact that 
in most of the recent accounts of synapsis and reduction in plants 
a side-by-side pairing of chromosomes from maternal and paternal 
spirems is described, while in Oenothera the members of a pair are 
arranged end to end on a single spirem; and (2) on differences in 
chromosome distribution during reduction in certain hybrids of 
Drosera and of Oenothera (see p. 25). If reduction took place in 
the same manner in both genera, the chromosome distribution during 
reduction in these hybrids with reference to the parental chromosome 
numbers should be the same in both, but this is not the case. 
3. Pairing between the definitive chromosomes during diakinesis 
and the prophase of the heterotypic mitosis does not always take place, 
owing to a weak attraction between the chromosomes. This allows 
irregularities of distribution in the heterotypic mitosis, so that both 
(unpaired) chromosomes belonging to one pair will occasionally enter 
the same daughter nucleus (see p. 26). Germ cells will thus arise, 
from which both members of a given pair of chromosomes are 
absent. 
4. If we assume qualitative differences between the chromosomes 
or parts of them, various types would be expected to originate in this 
manner, each of them lacking the ability to develop certain qualities 
possessed by the parent form. On this view the mutations of Oeno- 
thera Lamarckiana are an instance of a process of analysis by which 
from the parent form arises a series of types, each lacking in certain 
characters or capacities possessed by the parent. This hypothesis . 
would account for the absence of reversions among Oenothera 
mutants, and perhaps also for some of the peculiarities of hybridiza- 
tion in Oenothera. This matter will be considered at another time. 
This explanation does not apply to all the mutants, however; for 
example, O. gigas. 
