Fecundation in Orchidea and Asclepiadece. 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, 



1st, 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 Asclepiadeee is ruptured, and comes in contact with 

 the base of the stigma without leaving the cell of the anthera. 



3rdly, 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 Asclepiadeae, 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 boyaux, which, according to him, 

 make their appearance at the period of impregnation. 



5 c 2 XXXVI. De- 



