Fecundation in Orchidea and Asclepiadea. 717 



nular matter hanging to them. The remaining statements, 

 however, though essentially erroneous, are so far founded in 

 fact, that had Gleichen either opened or rather dilated the 

 opening which must have existed in the pollen mass when these 

 tubes were found hanging to it, and more carefully attended to 

 the state of the other parts of the flower when the mass was seen 

 implanted in the tube, he must necessarily have obtained a cor- 

 rect view of the whole structure, and consequently have greatly 

 advanced, — by at least half a century, — not only our knowledge 

 of this particular family, but also the general subject of vege- 

 table impregnation. 



In 1793, Christian Konrad Sprengel, who adopts the opinion 

 of Jacquin both with respect to the pollen masses and pentagonal 

 stigma, further states, that this stigma has a secreting upper sur- 

 face or apex, and is formed of two united bodies, each of which 

 conveys to its corresponding ovarium the fecundating matter, 

 consisting of the oily fluid which exudes from the surface of the 

 pollen mass. He also considers insects as here essentially neces- 

 sary in impregnation, which they effect by extracting, in a 

 manner particularly described, the pollen masses from 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 intoxicating secretion of 

 the nectaria*. 



In I8O9, an essay on Asclepiadeae was published in the first 

 volume of the Memoirs of the Wernerian Natural History So- 

 ciety, in which one of my principal objects was to establish the 

 opinion, more or less conjectural, of Adanson, Richard, Jussieu, 



* It may here be remarked, that the prevailing form of inflorescence in Asclepiadeae 

 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. 



and 



