Fecundation in Orchidee and Asclepiadea. TH - 
1829* has given a very interesting account of the structure of 
the pollen masses in Asclepiadez, from observations commenced 
in 1825, 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 appendage or cauda he considers 
analogous to the boyau of Amici and Brongniart, differing 
however in its forming an essential part of the grain in Ascle- 
piadez ; 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 probably applied to some part of the stigma. 
In the month of July last I examined several species of As- 
clepias, with reference to Mr. Bauer's drawings and Dr. Ehren- 
berg's account of the pollen ;—the first object, therefore, was to 
ascertain the structure of the pollen mass. 
Although on this subject my earliest observations essentially 
agreed with Mr. Bauer's figures of the mass, which represent it 
as having a subdivided cavity with a grain of pollen in each 
cell; yet a further examination had led me to adopt the opinion 
of 'freviranus and Ehrenberg, who describe its cavity as being 
undivided and filled with distinct grains. 
* Linnea iv. p. 94. 
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