MUTATIONS 1 1 7 



for over a period of four generations. . . . This ancestry was quite constant 

 as to the peloric peculiarity, remaining true to the wild type as it occurs 

 everywhere in any country, and showing in no respect any tendency to the 

 production of a new variety. 



[Second] the mutation took place at once. It was a sudden leap from 

 the normal plants with very rare peloric flowers to a type exclusively peloric. 

 The parents themselves had borne thousands of flowers during two summers, 

 and these were inspected nearly every day in the hope of finding some pelorics 

 and of saving their seed separately. Only one such flower was seen. . . . 

 There was simply no visible preparation for this sudden leap. 



This leap, on the other hand was full and complete. No reminiscence of 

 the former condition remained. Not a single flower on the mutated plant 

 reverted to the previous type. . . . The whole plant departed absolutely 

 from the old type of its progenitors. 



The next object was to seek for other mutants from the same 

 lot of seed l and to compare their proportion with the proportion 

 coming true from the seed of the first mutant. 



Accordingly De Vries planted his entire remaining stock of 

 seed, which, it will be remembered, was grown from the pair of 

 plants one of which bore a single peloric flower, but both of which 

 were immediately descended from the single five-spurred flower 

 of the third generation. 



From this seed he grew about two thousand plants in well- 

 manured soil. About 1750 of these bore flowers, and among 

 these sixteen, or about i per cent, were wholly peloric. As these 

 seeds were of the same generation that produced the first mutant, 

 he concludes that the chance of a peloric mutant is not over one 

 in a hundred. 



De Vries next undertook to determine whether the mutation 

 would be repeated in another generation, for up to this point all 

 the mutants had arisen from the same lot of seed. For this 

 purpose he saved seeds from normal plants so isolated as to pre- 

 vent crossing with peloric strains. In one instance he " obtained 

 two and in another one peloric plant with exclusively many- 

 spurred flowers," showing conclusively that mutations are itera- 

 tive, and that the same conditions that produce one mutant 

 will from time to time produce others altogether similar. 



1 It will be remembered that the original stock of seed of this generation was 

 10 cc., but that only enough had been grown to produce fifty plants, leaving a 

 quantity still on hand. 



