HYBRIDISM 2SS 



hand, one species in a group will sometimes resist great changes 

 of conditions with unimpaired fertility; and certain species in a 

 group will produce unusually fertile hybrids. No one can tell till 

 he tries, whether any particular animal will breed under confine- 

 ment, or any exotic plant seed freely under culture; nor can he 

 tell till he tries, whether any two species of a genus will produce 

 more or less sterile hybrids. Lastly, 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 sterility ensues. So it 

 is with hybrids, for their offspring in successive generations are 

 eminently liable to vary, as every experimentalist has observed. 



Thus we see that when organic beings are placed under new 

 and unnatural conditions, and when hybrids are produced by 

 the unnatural crossing of two species, the reproductive system, 

 independently of the general state of health, is affected in a very 

 similar manner. In the one case, the conditions of life have been 

 disturbed, though often in so slight a degree as to be inappreciable 

 by us; in the other case, or that of hybrids, the external condi- 

 tions have remained the same, but the organization has been dis- 

 turbed by two distinct structures and constitutions, including of 

 course the reproductive systems, having been blended into one. 

 For it is scarcely possible that two organizations should be com- 

 pounded into one, without some disturbance occurring in the 

 development, or periodical action, or mutual relations of the differ- 

 ent parts and organs one to another or to the conditions of life. 

 When hybrids are able to breed inter se, they transmit to their 

 offspring from generation to generation the same compounded 

 organization, and hence we need not be surprised that their steril- 

 ity, though in some degree variable, does not diminish; it is even 

 apt to increase, this being generally the result, as before explained, 

 of too close interbreeding. The above view of the sterility of 

 hybrids being caused by two constitutions being compounded into 

 one has been strongly maintained by Max Wichura. 



It must, however, be owned that we cannot understand, on the 

 above or any other view, several facts with respect to the sterility 

 of hybrids; for instance, the unequal fertihty of hybrids produced 

 from reciprocal crosses; or the increased sterility in those hybrids 

 which occasionally and exceptionally resemble closely either pure 

 parent. Nor do I pretend that the foregoing remarks go to the 

 root of the matter; no explanation is offered why an organism, 

 when placed under unnatural conditions, is rendered sterile. All 



