IN ORCHIDE^ AND ASCLEPIADEiE. 531 



addition consists in a modification or production of the 

 stigma ; the modified part of which loses the proper func- 

 tion of that organ. 



This production of the stigma, — which is generally 

 present, and wanting only in certain Orchidese, where its 

 place is sometimes supphed by an analogous modification 

 of the male organ^ — though differing, very remarkably in 

 appearance in the two families, agrees in being originally 

 distinct from the pollen masses, and in the advanced stage 

 becoming firmly attached to them ; in adhering but slightly 

 to the point of its formation after the attachment to the 

 pollen takes place ; and in being so constructed as to be 

 readily removed by insects from its original position along 

 with the pollen masses. 



As to the second point of agreement ; namely, the co- 

 hesion of the grains of pollen into masses of considerable 

 size, and the application of these masses to the stigma, — 

 it is obviously connected with that which might perhaps 

 be termed a third peculiarity ; the apparent necessity for 

 an imusual number of poUen tubes which are to act in 

 concert; in the one family to penetrate to and regularly 

 arrange themselves in the cavity of the ovarium -^ in the 

 other to open a communication with the stigma, and then 

 to pass along a non-secreting surface, until they arrive at a 

 distant point, where they are to be introduced into the 

 cavity or body of the style. 



With respect to the agency of Insects in fecundation in 

 those two orders, there can be no doubt that it is very fre- 

 quently employed in Orchidese ; at the same time there are 

 evidently cases in that family in which, from the relative [732 

 position of the organs, the interposition of these agents is 

 not always required. But in those Asclepiadese at least 

 that have been fully examined, the absolute necessity for 

 their assistance is manifest. 



Two questions still remain. 



The first regards the proof of the actual penetration of 

 the pollen tubes into the cavity of the ovarium in both 

 families. 



' See Additional Observations. 



