THE HUMAN PLANT 369 



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

 tion that there are limits of crossbreeding beyond 

 which the plant developer may not advanta- 

 geously 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, particularly in the second and later genera- 

 tions, 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. 



But it must be recalled that the plant devel- 

 oper always has full privilege of excluding the 

 undesirables from the hybrid fraternity. He 

 can pick out one or two individual hybrids 



