THE FACTORS OF EVOLUTION 207 



famarckiana. As long as one does not know the conditions 

 under which new species are produced it will always remain 

 difficult, according to De Vries, to find suitable material for 

 an experiment of this kind, and here chance must help to 

 smooth the way. 



In the 'eighties De Vries commenced to investigate the flora 

 in the environments of Amsterdam with the object of dis- 

 covering, if possible, a plant in the mutation stage. He was 

 fortunate enough to find what he wanted in 0. lamarckiana, 

 on a fallow potato-field near Hilversum. This plant had in 

 the course of ten years taken possession of more than half the 

 field in question. Among the many hundreds of individual plants 

 he observed in particular two forms which differed in so 

 many characters that they had to be regarded as new species. 

 They were afterwards described as 0. brevistylis and 0. Icevifolia, 

 and proved constant in cultivation. 



In order to obtain more accurate information concerning its 

 mutability, De Vries transplanted in 1886 a certain number of 

 roots and seeds from the potato-field into his experimental garden 

 at Amsterdam. In the course of several generations the seeds 

 of these first individuals produced, in addition to normal plants, 

 suddenly, by mutation, seven new species, which were described 

 as 0. lata, mbrinervis, gigas, albida, oblonga, nanella and 

 scintillans. With the exception of lata and scintillans all proved 

 to be constant under self-fertilization. The other forms do not 

 interest us, as they either produced no seed or could not be 

 sharply differentiated, but the history of one of these new species 

 is most instructive. 



In 1895, the fourth generation of the 0. lamarckiana , 14,000 

 seeds had been sown, of which the ' mutating ' individuals were 

 cultivated, but all others recognized as lamarckiana pulled up 

 to make room. In August about a thousand of these plants 

 were in bloom, but many had remained rosettes. Of these, thirty- 

 two of the most vigorous individuals were planted in a special 

 bed. In the following year they commenced to flower, and one 

 specimen at once attracted attention by its thicker stem, closer 

 inflorescence, and considerably larger flowers. Enclosed in a 

 parchment bag, it was artificially fertilized with its own pollen. 

 It produced a wealth of seed and formed the origin of a new 



