722 Mr. Brown on the Organs and Mode of 
I was confirmed in this opinion on considering the state of 
the mass after the production of the pollen tubes : for it appeared 
very improbable that the cells, unless they were of extreme 
tenuity, could be either suddenly removed or sufficiently rup- 
tured to admit of the passage of the tubes from its more distant 
parts to the point or line of dehiscence. 
The appearance however occasionally met with, of lacerated 
membranes proceeding, as it seemed, from the margins of the 
areolz of the inner surface of the mass, added to the facts which 
had originally led me to adopt Mr. Bauer's view, determined 
me to re-examine the subject. 
The result of this examination, made on specimens of Ascle- 
pias phytolaccoides and purpurascens, but especially the former, 
proved that the mass in these species is really cellular in all 
stages, as Mr. Bauer has represented it in A. curassavica, and 
that in the advanced flower-bud, as in the expanded flower, the 
cells may be seen, though not without difficulty, after their 
grains are removed. 
The pollen mass in several species of Asclepias, particularly 
in Asclepias phytolaccoides* (and in A. curassavica, as figured by 
Mr. Bauer), consists of cells disposed in three series parallel to 
its sides, the middle series being often more or less interrupted. 
The cells of the outer layer of each side have their oppo- 
site walls very unequal both in colour and thickness. The 
outer wall of each of these cells, which is formed by one of 
the areolz of the surface, is of a deep yellow colour, nearly 
opake, and of such thickness as to prevent external bursting ; 
the inner is of a paler yellow, semi-transparent, and so much 
thinner as to determine internal rupture, which ‘n these cells, 
after the production of the tubes, seems to take place without 
regularity, and to such an extent, that after the removal of 
* Tab. 35. fig. 8. 
the 
