Chap. VIII. OF FIRST CROSSES AND OF HYBRIDS. 251 



conditions with unimpaired fertility; and certain species in a 

 p^roiip will produce unusually fertile hybrids. No one can tell, 

 till he tries, whether any particular animal will breed under 

 confinement, 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. Lastl}^ 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 arc eminently liable to vary, as every 

 experimentalist has observed. 



Thus we s(>e 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 by 

 sterility in a very similar manner. In the one case, tlie condi- 

 tions of life have been disturbed, though ofteit in so slight a 

 degree as to be inappreciable by vis ; in the other case, or that 

 of hybrids, the external conditions have remained the same, 

 but the organization has been disturbed by two different struct- 

 ures and constitutions 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 de- 

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

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

 When hyl)rids are able to breed inter se, they transmit to their 

 offsj)ring from generation to generation the same compounded 

 organization, and hence we need not be surprised that their 

 sterility, thougli in some degree variable, does not diminish; it 

 is even a]it to increase, this being generally the result, as l)eforc 

 explained, of too close interbreeding. The above view of the 

 sterility of hybrids being caused by two different constitutions 

 being conlounded into one, has lately been strongly maintained 

 l)y Max Wichura ; but it must be owned that the sterility (as 

 will be immediately ex])lained) which affects the offspring of 

 dimorphic and trimorpliic plants, when individuals l)elonging 

 to the same form are united, makes this view rather doulitful. 

 It should, however, be borne in mind that the sterilitv of these 

 plants has been acfpiired for a special purpose, and may differ 

 in origin from that of hybrids. 



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



