NATURE AND CAUSES OF VARIATION 29 



The importance of mutations has been emphasised 

 by Professor de Vries of Amsterdam, and he has made 

 a special study of the subject. In the course of much 

 experimental work he was fortunate enough to find a 

 plant which was, as it were, producing mutations right 

 and left. This was the plant known as Lamarck's 

 Evening Primrose, which had been accidentally intro- 

 duced into Holland from America. De Vries found the 

 plant growing in a deserted potato-field in 1886, and 

 the following year he discovered two peculiar forms, 

 a smooth-leaved form and a type with a peculiarly 

 short style. De Vries removed stocks of these different 

 types to the botanical garden at Amsterdam, and there 

 proceeded to grow enormous numbers of seedlings. 

 Amongst these a large number of new mutations were 

 found a giant and a dwarf, a form with red-nerved 

 leaves, another with very broad leaves, and several 

 others. Altogether ten perfectly distinct new types 

 were discovered, all but one of which bred true from 

 seed. Some of these mutations were produced many 

 times, others only very rarely. 



These examples will serve to show what we mean by 

 the term mutation. We have given a few particular 

 instances, but it must not be imagined that only a 

 limited number of cases are known. A great number 

 of mutations have been described, and many of our 

 varieties of cultivated plants and domestic animals 

 have undoubtedly arisen in this way. 



It will readily be understood that only the appear- 

 ance of very marked novelties will tend to be recorded 

 in the ordinary course of events. Small changes will 

 tend to pass unnoticed, and when they occur in con- 

 junction with a considerable amount of other variation 

 they may be indistinguishable even to the trained 

 observer. But it is the modern view of variation 

 that all real changes in the nature of the germ plasm 

 are of the same kind. Whether they be large and strik- 

 ing or minute and hardly perceptible, the changes are 

 all of the nature of mutations sharp and definite steps 

 from one condition to another. Moreover, it is believed 



