IN ORCHIUE.® AND ASCLEPIAUE^. 53^ 



blished with the process or arm of the gland, which is then 

 very viscid, undergoes manifest changes, from being ventri- 

 cose and opaque becoming fiat, 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. His opinion, therefore, in every respect 

 agrees with that which originated with Richard and Jussien, 

 and which I had adopted. 



The celebrated traveller and naturalist, Dr. Ehrenberg, 

 in 1829,^ has given a very interesting account of the [721 

 structure of the pollen masses in Asclepiadese, from obser- 

 vations commenced in 1835, and others made in 1828. 



In this account he describes the pollen mass as consisting 

 of a proper 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 hoyau of 

 Amici and Bron gniart differing however in its forming an 

 essential part of the grain in Asclepiadese ; whereas in 

 other families the application of an external stimulus 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 applied 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 account of the pollen ; — the first object, there- 



' Linncea iv, p. 94. 



