690 Mutations 



microscopical iovestigations as well as extended 

 pedigree-cultures. The cooperation of many 

 workers is required to cover the field. Some- 

 where no doubt the desired principle lies hid- 

 den, but until it is discovered, all methods must 

 be tried. 



With this conception as the best starting- 

 point for further investigation, we may now 

 make a brief survey of the other phase of the 

 problem. We shall try to connect our observa- 

 tions on the evening-primroses with the theory 

 of descent at large. 



We start with two main facts. One is the 

 mutability of Lamarck's primrose, and the sec- 

 ond is the immutable condition of quite a num- 

 ber of other species. Among them are some 

 of its near allies, the common and the small- 

 flowered evening-primrose, or Oenothera bien- 

 nis and 0. muricata. 



From these facts, a very important question 

 arises in connection with the theory of descent. 

 Is the mutability of our evening-primroses tem- 

 porary, or is it a permanent condition? A dis- 

 cussion of this problem will give us the means of 

 reaching a definite idea as to the scope of our 

 inquiries. 



Let us consider the present first. If mutabil- 

 ity is a permanent condition, it has of course no 

 beginning, and moreover is not due to the 



