The Wallace-Darwin Correspondence 



results would have come out better had you always takeir 

 weights instead of heights; and that would have obviated 

 the objection that will, I daresay, be made, that height 

 proves nothing, because a tall plant may be weaker, less 

 bulky and less vigorous than a shorter one. Of course no 

 one who knows you or who takes a general view of your 

 results will say this, but I daresay it will be said. I am 

 afraid this book will not do much or anything to get rid 

 of the one great objection, that the physiological character- 

 istic of species, the infertility of hybrids, has not yet been 

 produced. Have you ever tried experiments with plants 

 (if any can be found) which for several centuries have 

 been grown under very different conditions, as for instance 

 potatoes on the high Andes and in Ireland? If any approach 

 to sterility occurred in mongrels between these it would be 

 a grand step. The most curious point you have brought out 

 seems to me the slight superiority of self -fertilisation over 

 fertilisation with another flower of the same plant, and the 

 most important result, that difference of constitution is the 

 essence of the benefit of cross-fertilisation. All you now 

 want is to find the neutral point where the benefit is at its 

 maximum, any greater difference being prejudicial. 



Hoping you may yet demonstrate this, believe me yours 

 very faithfully, Alfred R. Wallace. 



Rose Hill, Dorking. January 17, 1877. 



My dear Darwin, — Many thanks for your valuable new 

 edition of the ^^ Orchids," which I see contains a great deal 

 of new matter of the greatest interest. I am amazed at your 

 continuous work, but I suppose, after all these years of it, 

 it is impossible for you to remain idle. I, on the contrary, 

 am very idle, and feel inclined to do nothing but stroll about 

 this beautiful country, and read all kinds of miscellaneous 

 literature. 



