1865 i88i] F. MULLER 351 



Hedyotis^ is dimorphic in India ; the two other genera in the Letter 675 

 same sub-family with Villarsia are dimorphic in Europe and 

 Ceylon ; a sub-genus of Erythroxylon 2 is dimorphic in Ceylon, 

 and Oxalis with you and at the Cape of Good Hope. If 

 you can find a dimorphic Oxalis it will be a new point, for 

 all known species are trimorphic or monomorphic. The case 

 of Convolvulus will be new, if proved. I am doubtful about 

 Gesneria? and have been often myself deceived by varying 

 length of pistil. A difference in the size of the pollen-grains 

 would be conclusive evidence ; but in some cases experiments 

 by fertilisation can alone decide the point. As yet I know 

 of no case of dimorphism in flowers which are very irregular ; 

 such flowers being apparently always sufficiently visited and 

 crossed by insects. 



To F. M tiller. Letter 676 



Down, April 22nd [1867]. 



I am very sorry your papers on climbing plants never 

 reached you. They must be lost, but I put the stamps on 

 myself and I am sure they were right. I despatched on the 

 2Oth all the remaining copies, except one for myself. Your 

 letter of March 4th contained much interesting matter, but I 

 have to say this of all your letters. I am particularly glad 

 to hear that OnMium flexuosum* is endemic, for I always 

 thought that the cases of self-sterility with orchids in hot- 

 houses might have been caused by their unnatural conditions. 

 I am glad, also, to hear of the other analogous cases, all of 

 which I will give briefly in my book that is now printing. 

 The lessened number of good seeds in the self-fertilising 

 Epidendrums is to a certain extent a new case. You suggest 



1 Hedyotis was sent to Darwin by F. Miiller ; it seems possible, there- 

 fore, that Hedyotis was written by mistake for some other Rubiaceous 

 plant, perhaps Oldenlandia, which John Scott sent him from India. 



2 No doubt Sethia. 



3 Neither Convolvulus nor Gesneria have been shown to be dimorphic. 



4 See Animals and Plants, Ed. n., Vol. II., p. 114. Observations on 

 Oncidium were made by John Scott, and in Brazil by F. Miiller, who 

 " fertilised above one hundred flowers of the above-mentioned Oncidium 



flexuosum, which is there endemic, with its own pollen, and with that 



taken from distinct plants : all the former were sterile, whilst those 



fertilised by pollen from any other plant of the same species were 

 fertile." 



