14 OPHEE^?:. Chap. L 



poUinia of Orchis pyramidalis adhering to the pro- 

 boscis of a moth, with the stump-like caudicles alone 

 left, all the packets of poUen having been left glued 

 to the stigmas of the successively visited flowers. 



One or two other little points must be noticed. 

 The balls of viscid matter within the pouch-formed 

 rostellum are surrounded with fluid; and this is 

 very important, for, as already mentioned, the viscid 

 matter sets hard when exposed to the air for a very 

 short time. I have pulled the balls out of their 

 pouches, and found that they had entirely lost the 

 power of adhesion after a few minutes. Again, the 

 little discs of membrane, the movement of which, as 

 causing the movement of the poUinia, is so abso- 

 lutely indispensable for the fertilisation of the flower, 

 lie at the upper and back surface of the rostellum, 

 and are closely enfolded and thus kept damp within 

 the bases of the anther-cells ; and this is very neces- 

 sary, as an exposure of about thirty seconds causes 

 the movement of depression to take place ; but as 

 long as the disc is kept damp, the poUinia remain 

 ready for action whenever removed by an insect. 



Lastly, as I have shown, the pouch, after being 

 depressed, springs up to its former position ; and this 

 is likewise of great service ; for if this action did not 

 take place, and an insect after depressing the lip 

 failed to remove the two viscid balls, or if it removed 

 one alone, then in the first case both, and in the 

 second case one would be left exposed to the air; 

 consequently one or both would quickly lose all 

 adhesiveness, and the poUinium would be rendered ab- 

 solutely useless. That with many kinds of Orchids 

 insects often remove only one of the two poUinia at 

 a time is certain; it is even probable that they 

 generally remove only one, for the lower and older 



