706 
GENETICS: B. M. DAVIS 
established the fact that the two sets of chromosomes, derived one from 
each parent, constitute two series of homologous pairs and that the 
members of these pairs become closely associated before the reduction 
divisions and are later separated by this mitosis which may properly 
be termed a segregation division. 
Studies on the reduction divisions of O. Lamarckiana and some of its 
derivatives by Geerts, Gates, Stomps, Lutz and Davis have shown loose 
associations such that the mechanical conditions favor irregularities of 
distribution which actually do occur and gametes are known to be some- 
times formed with one more or one less chromosome than 7 which is 
the normal number for the genus. In the two 'mutants' lata and scin- 
tillans there have been observed 15 chromosomes, obviously the result 
of the union of gametes bearing unlike numbers of chromosomes. Forms 
with 21 chromosomes are also known which apparently arise from the 
fertilization of an unreduced egg (14 chromosomes) by a normal sperm 
nucleus (7 chromosomes). There is also a very rare type, gigas, with 
28 chromosomes which has been matched in chromosome number by 
analogous forms discovered by Bartlett from other species of Oenothera. 
This irregular behavior of the chromosomes in Lamarckiana and its 
'mutants' gives strong cytological evidence of conditions such as might 
be expected in heterozygous material where the two sets of chromo- 
somes from parental lines are dissimilar in their genetical constitution 
and consequently fail to pair closely previous to segregation through 
the reduction division. One of the Oenotheras, a race of grandiflora, 
has been found to present an orderly assembling of chromosomes in 
pairs at the time of reduction together with an equal distribution of 
the members of each pair and this history in one of the more stable 
forms serves to emphasize the striking irregularities of Lamarckiana. 
Therefore the cytological evidence is distinctly favorable to a view that 
Oenothera Lamarckiana contains a chromosomal complex of a mixed or 
hybrid character rather than two similar sets of chromosomes. 
On the genetical side there is more obvious evidence of the hetero- 
zygous nature of Oenothera Lamarckiana. It is a law of genetics that 
crosses between organisms which produce uniform gametes must give 
uniform progenies in the first generation and this constitutes a reliable 
test of whether or not the parents are monogametic; if the first hybrid 
generation contains distinct classes then one or the other or both of the 
parents must have produced more than one kind of fertile gametes. 
De Vries discovered the striking fact that when Lamarckiana and some 
of its mutants are crossed with certain wild species of Oenothera their 
