518 ON THE ORGANS AND MODE OF FECUNDATION 



In 1793, Christian Koiirad Sprengel, who adopts the 

 opinion of Jacquin both Avith respect to the pollen masses 

 and pentagonal stigma, further states, that this stigma has 

 a secreting upper surface or apex, and is formed of two 

 imited bodies, each of which conveys to its corresponding 

 ovarium the fecundatuig matter, consisting of the oily fluid 

 which exudes from the surface of the pollen mass. He 

 also considers insects as here essentially necessary in im- 

 pregnation, which they effect by extracting, in a manner 

 particularly described, the pollen masses f]jom the cells, 

 and applying them to the apex of the stigma. And lastly, 

 as extraordinary activity of the insect is necessary, or at 

 least advantageous in the performance of this operation, 

 that activity is, according to him, produced by the intoxi- 

 cating secretion of the nectaria.^ 



In 1809, an essay on Asclepiadese was published in the 

 first volume of the Memoirs of the Wernerian Natural 

 History Society, in which one of my principal objects M'as 

 to establish the opinion, more or less conjectural, of Adanson, 

 718] Richard, Jussieu, and Schreber, respecting the struc- 

 ture of the stamina and stigma. With this view I appealed 

 to the remarkable fact, that in the early state of the flower- 

 bud the pollen masses are absolutely distinct from the 

 glands and processes of the stigma, to which they in a 

 more advanced stage become attached. This proof of the 

 real origin of parts I then believed to be entirely new. It 

 lias, however, been already seen that the fact was noticed 

 by Gleichen, and it will presently appear that it was also 

 well known to another original observer. 



In the essay referred to, I had not very minutely ex- 

 amined the texture of the pollen mass, and in true Ascle- 

 piadeae I had failed in ascertaining its real internal struc- 

 ture ; not having been then aware of the existence of the 

 included grains of pollen, but believing, until very lately, 

 that the mass in its most advanced state consisted of one 



'. It may here be remarked, that the prevailing form of inflorescence in 

 Asclepiadese is well adapted to this economy ; for the insect so readily passes 

 from one corolla to another, that it not unfrequently visits every flower of the 

 umbel, 



