196 BOTANICAL GAZETTE [MARCH 
identical, strictly analogous to those which differentiate the wild 
species of the whole group. In some cases the differences are even 
larger. Those between the wild species are often very small and 
limited to certain life periods, leaving the species quite alike during 
the remainder of their development. No arguments have as yet 
been adduced to doubt the fundamental identity of the two groups 
of characters. 
6. The phenomenon of mutability, observed in O. Lamarckiana, 
O. biennis, and allied forms, is therefore to be considered as a simple 
continuance of the supposed mutability which presided at the 
origin of the wild species of the evening primroses. 
7. The seeds of the evening primroses are often very slow in 
germinating, leaving sometimes one half or more of the healthy 
germs in a dormant condition. This difficulty in the study of 
mutation percentages, etc., may be overcome by pressing the 
water into them. A pressure of 6-8 atmospheres during 1-3 days 
is ordinarily sufficient to stimulate all or almost all the good germs 
to a rapid germination. 
The microscopic preparations and the counts of chromosomes, 
referred to in this article, have been made for me by my assistant 
Mr. C. VAN OVEREEM, to whom I wish to give my sincere thanks 
for his cooperation. 
AMSTERDAM, HoLLAND 
