1S59-1S6.il TEGETMEIEU 223 



modified merely to favour crossing; with equal readiness it Letter 152 

 could be modified to prevent crossing. 



It is this which makes me so much interested with 

 dimorphism, etc. 1 



One word more. When you pitched me head over heels 

 by your new way of looking at the back side of variation, I 

 received assurance and strength by considering monsters — 

 due to law : horribly strange as they are, the monsters were 

 alive till at least when born. They differ at least as much 

 from the parent as any one mammal from another. 



I have just finished a long, weary chapter on simple facts 

 of variation of cultivated plants, and am now refreshing 

 myself with a paper on Linum for the Linn can Society. 



To W. B. Tegetmeier. Letter 153 



The following letter also bears on the question of the artificial 

 production of sterility. 



Down, 27th [Dec, 1S62]. 



The present plan is to try whether any existing breeds 

 happen to have acquired accidentally any degree of sterility ; 

 but to this point hereafter. The enclosed MS. will show 

 what I have done and know on the subject. Please at some 

 future time carefully return the MS. to me. If I were going 

 to try again, I would prefer Turbit with Carrier or Dragon. 



I will suggest an analogous experiment, which I have had 

 for two years in my experimental book with " be sure and 

 try," but which, as my health gets yearly weaker and weaker 

 and my other work increases, I suppose I shall never try. 

 Permit me to add that if £5 would cover the expenses of the 

 experiment, I should be delighted to give it, and you could 

 publish the result if there be any result. I crossed the Spanish 

 cock (your bird) and white Silk hen and got plenty of eggs 

 and chickens ; but two of them seemed to be quite sterile. I 



1 This gives a narrow impression of Darwin's interest in dimorphism. 

 The importance of his work was (briefly put) the proof that sterility has 

 no necessary connection with specific difference, but depends on sexual 

 differentiation independent of racial differences. See Life and Letters, 

 III., p. 296. His point of view that sterility is a selected quality is 

 again given in a letter to Huxley {Life and Letters, II., p. 384), but 

 was not upheld in his later writings (see Origin of Species, Ed. VI., p. 245). 

 The idea of sterility being a selected quality is interesting in connection 

 with Romanes' theory of physiological selection. (See Letters 209-214.) 



