228 Non-Isolablc Races. 



willingly agree with the prevailing view. In the sphere 

 of mutability, on the other hand, matters are entirely 

 ditlerent. Here species, subspecies, varieties, races, etc. 

 arise by mutations which are induced by rendering active 

 a hitherto latent or semi-latent character. The first con- 

 dition for a desired mutation therefore is the existence 

 of the character in question in a latent or semi-latent 

 state. Without this nothing can be achieved, at least in 

 the present state of science, and it is only in the case of 

 semi-latency that we can have any sort of evidence that 

 the desired character is present. Horticultural breeders 

 are well known to be continually on the lookout for any 

 such indication.^ 



But the presence of a latent character is not of itself 

 sufficient, according to my experience, to insure the suc- 

 cess of an experiment in selection. For many an experi- 

 ment has failed in spite of years of labor. 



This proves nothing in itself, because it is often due 

 to lack of sufficient experience, and this experience can 

 only be acquired by carrying out a successful experiment 

 in an analogous case ; in other words, by making exactly 

 the same experiment with a related plant, preferably 

 with another species of the same genus. 



For this reason I have more than once endeavored 

 to breed a race analogous to one already existing in a 

 closely related species of the same group, which is either 

 on the market, or has appeared in my own cultures. Ex- 

 perience has taught me that the end may often be attained 

 with greater or less ease according to circumstances; Init 

 that in many other cases, so it appears, insurmountable 

 obstacles bar the wav. 



A very definite and simple case is afforded by the 



* See Vol. T, Part T, § 25. p. 188; and this volume, Part I, § 2, p. 9. 



