INSECTS AND FLOWEKS : 1863 225 



enter by the toe and crawl out by the lateral windows. 

 -—I put in a small bee and it did so and came out with 

 its back smeared with pollen : I caught him and put him 

 in again, and again he crawled out by the window: 

 I out open the flower and found the stigma smeared 

 with pollen ! 



Read Bates Travels they will, I am sure, interest you. 

 — With respect to Fhysiantkus, I do not know whether 

 fact is known ; but I think it would be well worth 

 investigating.^ It is certain that the Asdepiadcn 

 require insect aid for fertilisation. The pollen-masses 

 are wonderfully like those of Orchids. You ought 

 to read R. Browns admirable paper on Asclepias in 

 Transact. Linnean Soc, about 15 or 20 years ago. In the 

 Apocyneas, (which are allied to the Asclepiadai) there 

 is a genus, which catches Diptera by the hundred : 

 I have a plant but cannot make it flourish, as I have 

 always wished to investigate the case. It is said that 

 the Diptera are caught by the wedge-shaped spaces 

 between filaments of anthers. But I suspect the plant 

 somehow profits or requires visits of insects. You ought 

 to try whether Physianthus will seed if insects are 

 excluded by a net. — I have seen Hymenoptera from 

 N. America with numbers of pollen-masses of some 

 Asclepias sticking to their tai-si ; ^ and the pollen-masses 



second edition (1877) he ^ves, on p. 230, Asa Gi-ay's view, and his 

 own observations confirming it. Mr. Francis Darwin has kindly 

 given me these references. 



'■ Darwin was here referring to a note of Trimen's about the 

 curious manner in which Lepidoptera and many other insects are 

 caught by a mechanical (not viscid) contrivance in the flowers of 

 Physianthus albens, — a native of temperate South America. It 

 seemed a case in which the plant overdid matters, the numerous 

 visitors being nipped by hard sharp ridges closing on the proboscis 

 when introduced into the nectaries, and the captives, in a great 

 many cases, failed to liberate themselves and carry off the 

 polUnia, eventually dying where they hung, 



^ I have myself often observed the difiBculty with which insects, 

 especially wasps and Fossors, dragged themselves free from the 



