INDIRECT BENEFITS DERIVED FROM INSECTS. 251 



AscIepiadecB that have been fully examined, the absolute 

 necessity for their assistance is manifest." 



Aristolochia clematitis, according to Professor Willdenow, 

 is so formed, that the anthers of themselves cannot impreg- 

 nate the stigma ; but this important affair is devolved upon a 

 particular species of gnat ( Cecidomyia pennicornis). The throat 

 of the flower is lined with dense hair, pointing downward, so as 

 to form a kind of funnel or entrance like that of some kinds of 

 mouse-traps, through which the insects may easily enter, but 

 not return ; several creep in, and, uneasy at their confinement, 

 are constantly moving to and fro, and so deposit the pollen 

 upon the stigma; but when the work entrusted to them is 

 completed, and impregnation has taken place, the hair which 

 prevented their escape shrinks, and adheres closely to the 

 sides of the flower, and these little go-betweens of Flora at 

 length leave their prison.^ Sir James Smith supposes that it 

 is for want of some insect of this kind that Aristolochia sipho 

 never forms fruit in this country. 



Equally important is the agency of insects in fructifying 

 the plants of the Linnean classes Monoecia, Dioecia, and Po- 

 lygamia, in which the stamens are in one blossom and the 

 pistil in another. In exploring these for honey and pollen, 

 which last is the food of several insects besides bees it be- 

 comes involved in the hair with which in many cases their 

 bodies seem provided for this express 23urpose, and is conveyed 

 to the germen requiring its fertilising influence. Sprengel 

 supposes that with this view some plants have particular in- 

 sects appropriated to them ; as to the dioecious nettle Cathe- 

 retes iirticce, to the toad-flax Catheretes gravidus, both minute 

 beetles, &c. Whether the operations of Cynips psenes be of 

 that advantage in fertilising the fig which the cultivators of 

 that fruit in the East have long supposed, is doubted by 



1 Grundriss der Krduterkitnde, 353. A writer, however, in the Annual 

 Medical Review (ii. 400. ) doubts the accuracy of this fact, on the ground tliat he 

 could never find C. pennicornis, though A. clematitis has produced fruit two years 

 at Brompton. Meigen (Dipt. i. 100. e.) places this amongst his doubtful 

 Cecidomyice. Fabricius considers it as a Chironomus. 



2 I have frequently observed Dermestes Jlavescens, Ent. Brit. (^Byturus') eat 

 both the petals and stamens of SUllaria holosteum ; and Mordellce will open the 

 anthers with the securiform joints of their palpi to get at the pollen. 



