78 
R. Ruggles Gates, 
CHAPTER III. 
Forms Having an Extra Chromosome. 
For a long time it was generally supposed that CE. lata and 
forms showing similar characters were the only ones containing an 
extra chromosome. Fifteen chromosomes had been announced in 
certain other forms by Miss Lutz (1908), but without convincing 
evidence. Then a very different form, CE. incurvata, having 15 
chromosomes, was described from the Swedish lamarckiana, 1 and 
Miss Lutz (1916, 1917) has more recently published her studies, 
which seem to show that the occurrence of mutations with an extra 
chromosome is much more frequent than was formerly supposed. 
Hance has also (1918) found 15 chromosomes in the mutant 
scintillans. This raises problems with regard to the relationship 
between these forms. 
It was natural to suggest that there might be seven distinct 
types in this series, 2 with a different chromosome of the haploid 
series figuring in each case. The number of types apparently with 
15 chromosomes is now considerably in excess of seven, but as will 
be observed from Table I, some of these appear to arise only from 
lata x lamarkiana. This is undoubtedly a significant fact. 
Now if we call the haploid series of chromosomes in 
(Enothera ABCDEFG and assume that A is the extra chromosome 
in lata , then its chromosome formula would be AAABBCCDDEE- 
FFGG ; and when the odd chromosome passes undivided to one 
pole in the reduction division without further irregularities, the 
gametes formed will be ABCDEFG and AABCDEFG. That is, 
there are three members of the A chromosome, two of which enter 
one gamete and one the other. It seems clear that such 
15-chromosome forms as semilata Gates, exilis, exundans and Miss 
Lutz’s typ6 5365 are derived through a secondary modification 
from lata. The evidence is strong that semilata Gates at any rate 
arises only from lata x lamarckiana. It appears very probable, 
on account of its characters intermediate between those of lata 
and lamarckiana, and also from its origin only from Lata , that the 
extra chromosome is the same in both. 
In order to have a different chromosome become the extra one 
in the sense in which it appears to be in lata , by selling this 
mutant (See Table 1), we must suppose that a gamete, which is, say, 
1 The Mutation Factor, p. 147. 
' l Gates and Thomas, 1914. 
