416 Origin of Each Species Considered Separately. 



given by a culture of strong biennial plants, carried out 

 with the utmost care (1897). Three of the figures, viz., 

 1, 2, 2% are afforded by too small crops to be of any 

 significance. On the other hand the cultures of 1895 and 

 1896 which involved 8000, 10,000 and 14,000 plants 

 respectively, and may therefore be relied on, gave 0.5, 

 1.7 and 1.8% apiece. These, then, are the most reliable 

 figures with which the rest, with the exception of the 

 first named (5%) agree very well. The remaining fig- 

 ures, which are 0.3—1—2—2—3—3—5—8 per 1000, 

 were either obtained in earlier years or in special cul- 

 tures. 



In the whole table there are 493 /a/a-mutants amongst 

 about 130,000 seedlings, or about 0.4%. 



§ 23. INCIPIENT SPECIES. 



According to the mutation theory, natural selection 

 chooses between species ; some are eliminated by it, others 

 permitted to increase and multiply. The new forms 

 arising from a single parent species by mutation may be 

 very numerous; they are often equally well equipped 

 for the struggle for existence being distinguished from 

 one another by characters which are unimportant in this 

 respect, as in the familiar case of Draba verna. 



But should there have arisen from Draba verna, be- 

 sides the elementary species now existing, others less 

 fitted for the struggle for existence, they would most 

 certainly have been eliminated sooner or later. And 

 there is no reason for supposing that elementary species 

 different from those now existing have not been pro- 

 duced. 



I have seen almost every year in my cultures of 



