Fecundation in Orchidee and Asclepiadee. 745 
edge of the pollen mass to the base of the stigma, its consequent 
dehiscence, the protrusion of the pollen tubes, and their pene- 
tration into the cavity of the style. 
The chief differences are, 
Ist, His not even suspecting the agency of insects in the 
fecundation of this family, and particularly in the plants ex- 
amined by him, in which I have regarded their assistance as 
absolutely necessary. 
2ndly, In his assuming that the pollen mass in these two 
genera of Asclepiadee is ruptured, and comes in contact with 
the base of the stigma without leaving the cell of the anthera. 
Srdly, His conjecturing that the secretion visible in the ex- 
panded flower on the angles of the stigma after removing the 
glands, is absorbed by the glands and conveyed through their 
arms or processes to the pollen mass, which it excites to the pro- 
duction of pollen tubes. 
Dr. Ehrenberg on the subject of Asclepiadex, repeats, with 
some slight modifications, his former statements quoted in my 
paper, and illustrates them by figures. In addition, he suspects 
that the pollen masses (which with Professor Link he regards as 
the true anthera, and the cells in which they are lodged as pro- 
cesses of the perigonium,) are not originally distinct from the 
glands of the stigma, regarded by him as the filaments of his 
supposed anthera. 
The central pentangular body he considers as the stigma, but 
he has no observations on the mode in which the pollen is 
applied to it. 
And lastly, His original statement respecting the grains of 
pollen is so far modified, that he now believes them to be in the 
early stages without tubes or boyaur, which, according to him, 
make their appearance at the period of impregnation. 
5c2 XXXVI. De- 
