Chap. IX. SECRETION OF NECTAR. 207 



the tender inner coat with their proboscides, and suck 

 the fluid contained in the inter-cellular spaces. This 

 conclusion has been Confirmed by Hermann Miillery 

 and I have further shown that even Lepidoptera are 

 able to penetrate other and tougher tissues. It is an 

 interesting case of co-adaptation that in all the British 

 species, in which the nectary does not contain free 

 nectar, the viscid matter of the disc of the polliniuni 

 requires a minute or two in order to set hard ; and 

 it would be an advantage to the plant if insects were 

 delayed thus long in obtaining the nectar by having 

 to puncture the nectary at several points. On the 

 other hand, in all the Ophrea? which have nectar ready 

 stored within the nectary, the discs are sufficiently 

 viscid for the attachment of the pollinia to insects, 

 without the matter quickly setting hard ; and there 

 would therefore be no advantage to these plants in 

 insects being delayed for a few minutes whilst sucking 

 the flowers. 



In the case of cultivated exotic Orchids which have 

 a nectary, without any free nectar, it is of course 

 impossible to feel absolutely sure that it would not 

 contain any under more natural conditions. Nor have 

 I made many comparative observations on the rate of 

 the settino; hard of the viscid matter of the disc in 

 exotic forms. Nevertheless it seems that some Yandea? 

 are in the same predicament as our British species of 

 Orchis ; thus Ccdanthe masuca has a very long nectary, 

 which in all the specimens examined by me was quite 

 dry internally, and was inhabited by powdery Cocci ; 

 but in the intercellular spaces between the two coats 

 there was much fluid ; and in this species the viscid 

 matter of the disc, after its surface had been disturbed, 

 entirely lost its adhesiveness in two minutes. In an 

 Oncidium the disc, similarly disturbed, became dry iu 



