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 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

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