THE SELF-FERTILIZATION OF PLANTS. 363 



does not result, in the other plants, to all of whose parts, 

 the conditions are unfavorable, in the degree in which 

 they are to most of the parts, in the sterile plants just 

 mentioned. Thus, favorable conditions, if favorable 

 only to one part or organ, will often produce loss of 

 fertility. Darwin in the quotation below, notes the 

 sterility of the plants, and sees that the conditions are, 

 in some way, answerable for the results ; yet, he can- 

 not imagine the mode, in which the conditions work 

 the effect ; but concludes that the sum of the knowable, 

 in this respect, is that the conditions are " unnatural!' 

 He says (p. 218, Animals and Plants, &c.) : 



" Plants, which have been exposed to unnatural 

 conditions, sometimes become modified, in so peculiar 

 a manner, that they are much more fertile, when 

 crossed by a distinct species, than when fertilized by 

 their own pollen." 



This explanation, that the "peculiar" manner, in 

 which they are modified, is due to conditions being 

 "unnatural" is to the full as satisfactory, and to the 

 full as scientific, as the explanation, that variations are 

 due to "an innate tendency to vary;" or, as the 

 explanation, that it is a " great law of nature," that evil 

 should attend close-interbreeding, and that good should 

 follow crossing. 



When plants, such as these which have been in 

 "unnatural conditions," are changed to other condi- 

 tions, and these other conditions are favorable to the 

 development of the parts which before were reduced or 

 suppressed, a gain in fertility naturally follows. 



"Returning to P. alata," says Darwin (p. 170, Vol. 



