723 Mr. BiiowN on the Organs and Mode of 



1 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 

 areolae 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 areolae 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 in 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 



