IN OUCIIIDE-E AND ASCLEPIADE.E. 52 



blislied with the process or arm of the gland, which is tlien 

 very viscid, undergoes manifest clianges, from being ventri- 

 cose and opaque becoming flat, hard, and transparent. 

 These changes he thinks are probably owing to the extrac- 

 tion of its fecundating matter by the process through 

 which it passes to the glands, and by them to the angles of 

 the stigma, whence it may be easily communicated to the 

 styles and ovaria. Ilis opinion, therefore, in every respect 

 agrees with that which originated with Richard and Jussieu, 

 and which I had adopted. 



The celebrated traveller and naturalist, Dr. Ehrenberg, 

 in I'^^l),^ has given a very interesting account of the [721 

 structure of the pollen masses in Asclepiadea), from obser- 

 vations commenced in 1S.:25, and others made in 1S.2S. 



In this account he describes the pollen mass as consisting 

 of a })roper membrane bursting in a regular manner, the 

 cavity being not cellular but undivided and filled with 

 grains of pollen, each grain having a cauda or cylindrical 

 tube often of great length, and all these tubes being 

 directed towards the point or line of dehiscence. This ap- 

 pendage or Cauda he considers analogous to the hojjau, of 

 Amici and Brongniart differing however in its forming an 

 essential part of the grain in Asclepiadere ; whereas in 

 other families the application of an external stinudus is 

 necessary for its production. 



He is entirely silent as to the manner in which these 

 caudate grains communicate with or act upon the stigma ; 

 and does not in any case remark, — what must, I think, 

 have been the fact, at least in several of the plants in which 

 this structure was observed, and especially in those with 

 pendulous pollen, — that the mass examined was no longer 

 in the cell of the anthera, but had been removed and pro- 

 bably a])])lied to some part of the stigma. 



In the month of July last I examined several species of 

 Asclepias, with reference to Mr. Bauer's drawings and Dr. 

 Ehrenberg's accoiuit of the pollen ; — the first object, there- 



' Limupa iv, p. 9L 



