INDIRECT BENEFITS DERIVED FROM INSECTS. 249 



the fly, it intended to avail itself of the tube of the leaf in- 

 stead of a burrow. Yet we know of no such strange deviation 

 from natural instinct, which would be the more remarkable, 

 because the insect was European, while the plant was Ame- 

 rican, and growing in a hot-house. And, at any rate, it does 

 not seem very likely that the insect would commit her egg to 

 the tube without having previously examined it; in which 

 case she must have discovered it to be half full of water, and 

 consequently unfit for her purpose. It is not so wonderful 

 that many large flies should, as Professor Barton informs us, 

 drop their eggs into the Ascidia furnished with dead carcasses; 

 and it seems very probable that Dytisci oviposit in them; for 

 the Squilhy which Rumphius found there, was probably one of 

 their larvae, this being the old name for them. ^ 



However problematical the agency of insects caught by 

 plants as to their nutriment, there can be no doubt that many 

 species perform an important function with regard to their 

 impregnation, which indeed without their aid would in some 

 cases never take place at all. Thus, for the due fertilisation 

 of the common Barberry {Berheris vulgaris), it is necessary that 

 the irritable stamens should be brought into contact with the 

 pistil by the application of some stimulus to the base of the 

 filament ; but this would never take place were not insects at- 

 tracted by the melliferous glands of the flower to insinuate 

 themselves amongst the filaments, and thus, while seeking 

 their own food, unknowingly fulfil the intentions of nature 

 in another department. ' 



The agency of these little operators is not less indispens- 

 able in the beautiful tribe of Iris. In these, as appears from 

 the observations of Kolreuter, the true stigma is situated 

 on the upper side of a transverse membrane {arcus eminens 

 of Haller), which is stretched across the middle of the under 

 surface of the petal-like expansion or style-flag, the whole 

 of which has been often improperly regarded as fulfilling 

 the ofiice of a stigma. Now, as the anther is situated 

 at the base of the style-flag which covers it, at a con- 

 siderable distance from the stigma, and at the same time 



1 MoufFet, 319. ^ 2 Smith's Tracts, 165. Kolreuter, Ann. of Bot. ii. 9. 



