PRESENT TENDENCIES OF MORPHOLOGY 277 



disciples of Darwin (Romanes, Weismann) had fallen. 1 Guided by 

 his earlier studies concerning the Galtonian curves and impressed 

 with the constancy of certain forms, such as the species described 

 by the botanist Jordan, whose origin was difficult to explain by fluc- 

 tuations, De Vries supposed that after periods of relative fixity during 

 which they are subject only to fluctuating variations, living beings 

 may pass through shorter periods when their forms are abruptly 

 modified in different directions by discontinuous changes. 



Biologists clearly recognized this kind of variation in what they 

 call sports. De Vries has called them mutations and he has shown the 

 importance of mutability especially in the study of a biannual plant, 

 (Enothera Lamarckiana, an American species introduced into Europe, 

 especially into many localities of the Low Countries. From 1880 to 

 1899 each year De Vries has planted in the botanical garden at Am- 

 sterdam from 15,000 to 20,000 seeds of this plant. Besides thou- 

 sands of normal individuals, his cultures have produced seven new 

 types, represented each year by a variable number of individuals and 

 capable of reproducing themselves by seed with great regularity. 

 Among the 50,000 (Enothera plants that he has observed during ten 

 years De Vries has counted 800 that might legitimately be called (Eno- 

 thera Lamarckiana, but which are divided as we have just said into 

 seven groups, to which it was fitting to give the systematic value 

 of subspecies, as the botanists would not have failed to do if these 

 plants had been found in the fields where their origin was not known. 



A great number of biologists have believed that they found in the 

 splendid studies of De Vries unanswerable arguments against the 

 theory of selection. It is impossible for me to share their opinion. I 

 should say even that in examining the question closely and in penetrat- 

 ing to the bottom of the matter, it is impossible for me to find in the 

 theory of mutations anything except a useful complement of the La- 

 marckian and Darwinian doctrine of continuous variation. 



As the economist Bastiat has said, in all complex phenomena where 

 multiple causes intervene in different ways, there is that which we 

 see and there is also that which we do not see. 



What we see in a mutation is the abrupt and sudden appearance of 

 a character which did not previously exist, but this character is only 

 the sudden manifestation of a state which has been prepared very 

 slowly in the ancestors of the individuals in which it appeared. In 

 order to obtain a chemical reaction, in order to cause the color of a 

 liquid to change, it is often necessary to add the reagent drop by drop, 

 until an instant when all at once the reaction occurs and the new 

 color appears. The mutation is the result of a new state of equilibrium 

 in the varying organism. All the individuals in which this new equi- 

 librium appears are in a different state internally from that of their 

 1 H. de Vries, Die Mutationstheorie, Leipzig, 1901-03. 



