176 VANDE^. Chap. VI. 



of the pollen -mass glued to its back. The insect then 

 generally gets through the passage, and comes out 

 with this peculiar appendage, to return nearly imme- 

 diately to its feast, when it is generally precipitated a 

 second time into the bucket, passing out through the 

 same opening, and so inserting the pollen-masses into 

 the stigma while it forces its way out, and thereby im- 

 pregnating either the same or some other flower. I 

 have often seen this ; and sometimes there are so many 

 of these humble-bees assembled that there is a continual 

 procession of them through the passage specified." 



There cannot be the least doubt that the fertilisation 

 of the flower absolutely depends on insects crawling 

 out through the passage formed by the extremity of 

 the labellum and the over-arching column. If the 

 large distal portion of the labellum or bucket had been 

 dry, the bees could easily have escaped by flying away. 

 Therefore we must believe that the fluid is secreted by 

 the appendages in such extraordinary quantity and is 

 collected in the bucket, not as a palatable attraction 

 for the bees, as these are known to gnaw the labellum, 

 but for the sake of wetting their wings, and thus 

 compelling them to crawl out through the passage. 



I have now described, perhaps in too much detail, 

 a few of the many contrivances by which the VandesB 

 are fertilised. The relative position and shape of the 

 parts — friction, viscidity, elastic and hygrometric move-v 

 ments, all nicely related to one another — come into 

 play. But all these appliances are subordinate to the 

 aid of insects. Without their aid, not a plant belong- 

 ing to this tribe, in the species of the twenty-nine 

 genera examined by me, would set a seed. It is also 

 certain in a majority of the cases, that insects withdraw 

 the poUinia only when retreating from the flower, and 



