404 BRITISH FLOWERING PLANTS chap. 



the spur is very delicate, and the cellular tissue ex- 

 tremely juicy, he suspected that insects possibly pierce 

 the membrane, and suck the juicy sap lying beneath. 

 His suggestion has been confirmed by H. Miiller, and he 

 himself in a subsequent memoir ' speaks confidently on 

 the point. Delpino, on the contrary, is confident that 

 the species examined by him ( 0. sambucina, O. Morio, 

 O. mascula, and O. maculata) do not secrete honey 

 either on or under the epidermis. The weight of 

 evidence, however, seems to be on the side of the 

 suggestion made by Darwin. Considering, he observes, 

 the incalculable number of plants which have been 

 fertilised, " we cannot believe in so gigantic an im- 

 posture." The case of some flies is different, as they 

 appear to be very stupid. To test the intelligence of 

 moths he tried an ingenious experiment. He cut off 

 about half the spur of six flowers out of twenty-one 

 on a spike, and found that while thirteen out of the 

 fifteen intact flowers had the poUinia removed, this was 

 only the case with half of those with their nectaries 

 removed. The result, however, though suggestive is 

 not conclusive ; and to make out a strong case the 

 experiment would have to be tried on a larger scale. 



However this may be, there is no doubt that the 

 tissues between the two membranes of the nectary in 

 O. pyramidalis contain a copious fluid ; on the other 

 hand, in allied species the spur of which contains abun- 

 dance of nectar, as, for instance, Gymnadenia conopsea 

 and Habenaria hifolia, the two membranes are close 

 to one another. Darwin makes an ingenious sugges- 

 tion to account for the diflerence. In the two latter 

 species the disk is naked and remains permanently 

 viscid. On the other hand, in O. pyramidalis the disk 

 is covered with a pouch. When this is pushed away by 

 an insect the disk rapidly becomes viscid, and gets hard 

 in a few minutes. It would therefore be an advantage 

 that the proboscis should be retained in place for a 

 short time, so that the viscid matter might have time 



' Arm. and Mag. of Nat. Hist., 1869. 



