296 INDIRECT BENEFITS DERIVED FROM INSECTS. 



with dead carcases : and it seems very probable that 

 Dytisci oviposit in them ; for the Squilla which Rumphius 

 found there was probably one of their larvae, this being 

 the old name for them a . 



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 fertilization of the common Barberry (Ber- 

 beris 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 attracted 

 by the melliferous glands of the flower to insinuate them- 

 selves amongst the filaments, and thus, while seeking 

 their own food, unknowingly fulfill the intentions of na- 

 ture in another department 5 . 



The agency of these little operators is not less indis- 

 pensable 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 impro- 

 perly regarded as fulfilling the office of a stigma. Now 

 as the anther is situated at the base of the style-flag which 

 covers it, at a considerable distance from the stigma, and 

 at the same time cut off from all access to it, by the in- 

 tervening barrier formed by the arcus eminens, it is clear 

 that but for some extraneous agency the pollen could 

 never possibly arrive at the place of its destination. In this 

 a Mouffbt, 319. b Smith's Tracts, 1 65. Kolreuler, Ann. of Bot. ii. 9. 



