TN OECHIDEjE and ASCLEPIADEjE. 533 



tubes have finished their growth, would afford an argu- 

 ment of some weight at least against their essentia] impor- 

 tance in any case ; and it may be added, that in Ascle- 

 piadese there appears to be no other source of nourishment 

 for the tube until it has penetrated into the style, than 

 these granules. Nor is it necessary to suppose that the 

 tabes themselves act directly, it being even probable that 

 they also contain a fluid or granular matter much more 

 minute than that originally filling the cavity of the grain.^ 

 Our knowledge indeed appears to me not yet sufficient 

 to warrant even conjectures as to the form of the imme- 

 diate agent derived from the male organ, or the manner of 

 its application to the ovulum in the production of that 

 series of changes constituting fecundation. I may, how- 

 ever, be allowed to observe, that at present, with respect 

 to this function, we are at least as far advanced in these 

 two families, hitherto considered so obscure, as we are in 

 any other tribe of Phsenogamous plants : and I even 

 venture to add, that in investigating the obscure subject of 

 generation, additional light is perhaps more likely to be 

 derived from a further minute and patient examination of 

 the structure and action of the sexual organs in Asclepia- 

 deee and Orchideae, than from that of any other department 

 either of the vegetable or animal kingdom. 



' See Additional Observations. 



