Mutations and Evolution. 
81 
have 15 chromosomes. De Vries showed (1909, Vol. I, p. 244) 
that this form also behaves in a peculiar way in inheritance, usually 
giving rise to an average of about 57% Lamarckiana, 32% scintillans 
9% oblonga and 1% lata. In one family as much as 69% scintillans 
was obtained. It is significant that several of the original scintillans 
mutants were from lata pollinated by Lamarckiana. From these 
results it would appear that scintillans originates from the union of 
two germ cells, one carrying 8 chromosomes and the other (or 
perhaps the same one) carrying the oblonga qualities. On the other 
hand, it is possible that the oblonga type to which it gives rise, has 
16 chromosomes, as Miss Lutz (1917) suggests. Also, while lata 
had a mutation frequency in de Vries’ cultures of 0*413%, the 
frequency of scintillans was only 0*038%. 
As predicted in 1915, 1 the cytological study of scintillans , 
resulting in the determination of an extra chromosome in its nuclei, 
throws much light on its origin and behaviour. It seems reasonable 
to interpret scintillans as arising from a germ cell with an extra 
chromosome—onebearing the oblonga characters—just aswe picture 
lata arising from a germ cell with an extra chromosome and one 
having the typical Lamarckiana characters. This will depend, 
however, on the chromosome counts in the various oblonga types, 
which are at present uncertain. That the offspring of scintillans 
were always found to include 1% or more lata , shows a close 
relationship between these two types, and indicates, though it does 
not prove, that the extra chromosome may be the same one in both 
cases. Another alternative is that any chromosome, if present in 
duplicate in a germ cell owing to non-disjunction in the reduction 
division, will give the lata features if combined with a Lamarckiana 
germ cell or scintillans if combined with an oblonga germ cell. 
This is improbable for many reasons. 
In regard to the relation between these forms, lata , semilata , 
and scintillans , we thus appeared at one time to be left with only 
two alternatives, either that the extra chromosome is the same in 
every case, as the breeding data suggest, 2 or that any of the 7 
haploid chromosomes when duplicated will give the same 
morphological result. The latter alternative is highly improbable 
for general cytological reasons. However, while the frequency of 
lata is certainly greater in the offspring of scintillans than of 
Lamarckiana , it is conceivable that its unbalanced condition may 
lead to more frequent chromosome irregularities. 
1 The Mutation Factor, p. 142. 
2 It seems highly probable that in lata and semilata at least, the extra 
chromosome is the same. 
