MUTATION THEORY OF DE VRIES 93 



stock — partly as plants and partly as seeds — from the potato- 

 field at Hilversum to the botanic garden at Amsterdam. 



The three stocks gave rise under cultivation to many thousands 

 of individuals, which bred true along certain lines, and yet gave 

 rise to other new forms. In short, De Vries had found a plant in 

 process of evolution. The predisposition to mutability — which 

 remains a mystery — was present, De Vries gave it scope, and 

 like the primeval gardener he had the pleasure of giving names 

 to a crop of new creations which emerged before him. From each 

 of his three samples there arose several distinctive groups — which 

 if they had been found in nature would have been reckoned as 

 distinct species of evening primrose. But the most interesting 

 feature was the apparent abruptness in the origin of the new 

 forms. They seemed to arise by leaps and bounds, by organic 

 jerks ; they illustrated what De Vries has called " Mutation." 



Besides the smooth-leaved O. Icevifolia and the short-styled 

 O. brevistylis, both of which appeared in the potato-field, the culti- 

 vation of O. lamarckiana resulted in the emergence of seven constant 

 elementary species — O. gigas (rare), O. rubrinervis, O. oblongata, 

 O. albida, O. leptocarpa, O. lata, and a dwarf O. nanella. Besides 

 these there were a few inconstant variants and a few which were 

 sterile. 



One form, 0. scintillans, that only appeared eight times, was not 

 constant like the others. When self-fertilised it produced O. ob- 

 longata, O. lamarckiana, and others like itself. 



It is interesting to notice that some of the forms — e.g. O. oblongata, 

 — were produced over and over again ; that five of the new forms 

 appeared afterwards in the field or from seeds collected in the field, 

 which shows that the cause of their origin was not to be found in the 

 cultivation. 



As De Vries says, the new elementary species arise suddenly 

 without transitional hnks ; for the most part they are quite 

 constant ; within the limits of their essential constancy they 

 exhibit similar minor fluctuations ; they are usually represented 

 by numerous individuals within the same period of time ; the 



