PLANT HYBRIDIZATION BEFORE MENDEL 233 



"Thus," Darwin says, "when organic beings are placed during several 

 generations under conditions not natural to them, they are extremely 

 liable to vary, which seems to be partly due to their reproductive systems 

 having been specially affected, though in a lesser degree than when ste- 

 rility ensues. So it is with hybrids, for their offspring in successive 

 generations are eminently liable to vary, as every experimentalist 

 knows." (la, 2: 26.) 



And further : 



"Now hybrids in the first generation are descended from species (ex- 

 cluding those long cultivated) which have not had their reproductive 

 systems seriously affected, and their descendants are highly variable." 

 (la, 2:41.) 



Darwin deserves credit for stoutly contesting the point of view 

 then widely current that the longer a character is handed down 

 by a breed, the more force per se it will carry in the transmission. 

 Discussing some of the cases, he says : 



"in none of these, nor in the following cases, does there appear to be 

 any relation between the force with which a character is transmitted and 

 the length of time during which it has been transmitted." (ic, 2:37.) 



The basis for such a view, that the longer a strain is grown, 

 and the more it is selected, the more uniform, i.e., the more ho- 

 mozygous, it becomes, was not scientifically known in Darwin's 

 time, but Darwin acutely perceived that the mere repeated act of 

 selection itself, whatever else might be involved, would not nec- 

 essarily increase the "potency" of transmission. 



Darwin's view as to the reason for the good effects of crossing 

 was based upon the long prevalent opinion that, since animals, 

 and hence presumably plants, profit from changes in their condi- 

 tions, probably such changes operate to affect the germ cells, or 

 that in some way the germ cells receive an extra stimulation on 

 that account which redounds to the benefit of the offspring, 

 (ic, 2:155.) 



So far as variability is concerned, Darwin holds : 



"That variability of every kind is directly or indirectly caused by 

 changed conditions of life. Or, to put the case from another point of 

 view, if it were possible to expose all the individuals of a species during 

 many generations to absolutely uniform conditions of life, there would 

 be no variability." (ic, 2:234.) 



Darwin quotes Pallas to the effect that all variation is due to 

 crossing, to which view, however, he opposed the facts of bud- 

 variation. It remained Darwin's view, as it was that of practically 



