26 THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 



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 0. Lamarckiana, 

 0. 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 1 wish to give my sincere thanks 

 for his cooperation. 



Amsterdam. 



(The Botanical Gazette, Vol. LIX, March 1Q15, p. i6g.) 



