IMPROVING THE HUMAN PLANT 



That such mixing of racial strains, within cer- 

 tain limitations, is likely to result in the develop- 

 ment of exceptional individuals will not be doubted 

 by any student of the subject, least of all by the 

 plant developer who has produced striking results 

 by a corresponding mingling of divergent types. 



But, on the other hand, it cannot escape atten- 

 tion that there are limits of crossbreeding beyond 

 which the plant developer may not advantageously 

 go. If he attempts to combine species of plants 

 that are too widely divergent, he either gets no 

 result or produces inferior progeny. And if the 

 races that are crossed lie just at the limits of 

 affinity, he may produce a progeny, that, particu- 

 larly in the second and later generations, become 

 so variable and diversified as to run counter in the 

 main to all of his plans and expectations. 



We have seen this illustrated in many cases 

 witness, for instance, the crossing of the tobacco 

 and the petunia, of the European and Chinese 

 quinces, of the oriental and opium poppies, and of 

 the various members of the genus Rubus. 

 THE NEED OF SELECTION 



In some of these cases, to be sure, individual 

 forms were produced that had very exceptional 

 interest and that might even supply material highly 

 prized by the plant developer for the production 

 of new races. 



[229] 



