1865 1881] F. MULLER 347 



Acropera now in flower, and have no doubt that some insect, Letter 673 

 with a tuft of hairs on its tail, removes by the tuft, the pollinia, 

 and inserts the little viscid cap and the long pedicel into the 

 narrow stigmatic cavity, and leaves it there with the pollen- 

 masses in close contact with, but not inserted into, the stig- 

 matic cavity. I find I can thus fertilise the flowers, and so 

 I can with Stanhopea, and I suspect that this is the case with 

 your Notylia. But I have lately had an orchis in flower 

 viz. Acineta, which I could not anyhow fertilise. Dr. Hilde- 

 brand lately wrote a paper 1 showing that with some orchids 

 the ovules are not mature and are not fertilised until months 

 after the pollen-tubes have penetrated the column, and you 

 have independently observed the same fact, which I never 

 suspected in the case of Acropera. The column of such 

 orchids must act almost like the spermatheca of insects. 

 Your orchis with two leaf-like stigmas is new to me ; but 

 I feel guilty at your wasting your valuable time in making 

 such beautiful drawings for my amusement 



Your observations on those plants being sterile which grow 

 separately, or flower earlier than others, are very interesting 

 to me : they would be worth experimenting on with other 

 individuals. I shall give in my next book several cases of 

 individual plants being sterile with their own pollen. I have 

 actually got on my list EscJischoltzia 2 for fertilising with its 

 own pollen, though I did not suspect it would prove sterile, 

 and I will try next summer. My object is to compare the 

 rate of growth of plants raised from seed fertilised by pollen 

 from the same flower and by pollen from a distinct plant, and 

 I think from what I have seen I shall arrive at interesting 

 results. Dr. Hildebrand 3 has lately described a curious case 

 of Corydalis cava which is quite sterile with its own pollen, 

 but fertile with pollen of any other individual plant of the 

 species. What I meant in my paper on Linum about plants 

 being dimorphic in function alone, was that they should be 

 divided into two equal bodies functionally but not structurally 

 different. I have been much interested by what you say on 

 seeds which adhere to the valves being rendered conspicuous. 



1 Bot. Zeitung, 1863, 1865. 



2 See Animals and Plants, II Ed. II., p. 118. 



3 Inter?iat. Hort. Congress, London, 1866, quoted in Variation of 

 Animals and Plants, Ed. II., Vol. II., p. 113. 



