3$4 BOTANY [Chap. XI 



Letter 678 me much. I am convinced that if you can prove that a plant 

 growing in a distant place under different conditions is more 

 effective in fertilisation than one growing close by, you will 

 make a great step in the essence of sexual reproduction. 



Prof. Asa Gray and Dr. Hooker have been staying here, 

 and, oddly enough, they knew nothing of your paper on 

 Martha} though the former was aware of the curious move- 

 ments of the stamens, but so little understood the structure 

 of the plant that he thought it was probably a dimorphic 

 species. Accordingly, I showed them your drawings and 

 gave them a little lecture, and they were perfectly charmed 

 with your account. Hildebrand 2 has repeated his experi- 

 ments on potatoes, and so have I, but this summer with no 

 result. 



Letter 679 To F. M tiller. 



Down, March 14th [1869]. 



I received some time ago a very interesting letter from 

 you with many facts about Oxalis, and about the non-seeding 

 and spreading of one species. I may mention that our 

 common O. acetosella varies much in length of pistils and 

 stamens, so that I at first thought it was certainly dimorphic, 

 but proved it by experiment not to be so. Boiseria 3 has after 

 all seeded well with me when crossed by opposite form, but 

 very sparingly when self-fertilised. Your case of Faraviea 4 



foreshadowing of the generalisation arrived at in Cross and Self-Fertilisa- 

 tion. Muller wrote : " Are the three which grow near each other 

 seedlings from the same mother-plant or perhaps from seeds of the same 

 capsule ? Or have they, from growing in the same place and under the 

 same conditions, become so like each other that the pollen of one has 

 hardly any more effect on the others than their own pollen ? Or, on the 

 contrary, were the plants originally one— i.e., are they suckers from a 

 single stock, which have gained a slight degree of mutual fertility in the 

 course of an independent life ? Or, lastly, is the result ' ein neckische 

 Zufall.' " (The above is a free translation of Midler's words.) 



1 F. Muller has described (Bot. Zeitung, 1866, p. 129) the explosive 

 mechanism by which the pollen is distributed in Martha (Posoquetia) 

 fragrans. He also gives an account of the remarkable arrangement for 

 ensuring cross-fertilisation. See Forms of Flowers, Ed. II., p. 131. 



3 See Letter 206, Vol. I. 



3 This perhaps refers to Boissiera {Ladizabala). 



4 See Forms of Flowers, Ed. II., p. 129. Faramea is placed among 

 the dimorphic species. 



