124 Gager, — The Development of the Pollinium and 
1805, and representing ‘the internal structure of the pollen- 
mass as cellular; each cell in the flower-bud just before 
expansion being filled with a grain of pollen, . . . while in the 
expanded flower this grain is exhibited as shrivelled, having 
discharged its contents, which consist of a mixture of an oily- 
fluid and minute granules V 
Link considered the pollen-mass as ‘ composed either of 
a cellular tissue, or manifestly of grains of pollen : the former 
part of the description being no doubt meant to apply to true 
Asclepiadeae, the latter to the Periploceae V 
In 1827 Treviranus described the pollen-mass of A. curassa- 
vica as ‘ filled with compressed, nearly round but obtusely 
angular, colourless, simple grains, containing minute granules ; 
the pressure of the external grains, or those in contact with 
the general covering, giving it the appearance of being 
cellular V 
Ehrenberg 3 (1829) describes the pollen-mass as ‘consisting 
of a proper membrane bursting in a regular manner, the 
cavity being not cellular but filled with grains of pollen, 
each grain having a cauda or cylindrical tube often of great 
length, and all the tubes being directed towards the point 
or line of dehiscence.’ This appendage he considers analogous 
to the ‘boyau ’ of Amici (1824) and Brongniart (1827), differ- 
ing, however, in its forming an essential part of the grain in 
Asclepiadeae ; whereas in other families the application of an 
external stimulus is necessary for its production. Later, 
Ehrenberg 3 (1831) believes that the grains of pollen are in 
their earlier stages without the ‘ boyaux,’ which make their 
appearance subsequently at the period of impregnation. 
In 1833, as a result of further researches on the Asclepiadeae, 
Brown describes the pollen-mass in several species of Asclepias , 
particularly in A . phytolaccoides and A. curassavica, the figures 
being drawn by Bauer. According to the description and 
figures, the pollen-mass consists of cells disposed in three 
series parallel to its sides, the middle series being often more 
1 Brown (1831), p. 719. 2 Brown, loc. cit, p. 730 . 
3 Quoted by Brown (1831). 
