204 INDIRECT BENEFITS DERIVED FROM INSECTS. 



insects indespensable in fructifying the different species of Iris, but that 

 some of them, as 1. xiphium, require the agency of the larger humble- 

 bees, which alone are strong enough to force their way beneath the style- 

 flaff ; and hence, as these insects are not so common as many others, this 

 Iris is often barren, or bears imperfect seeds. ^ Sprengel also contends, 

 that insects are essentially necessary in the impregnation of AsclepiadecB ; 

 in which opinion he is confirmed by the conclusive testimony of the cele- 

 brated botanist Robert Brown, Esq., who states^ that there can be no 

 doubt that the agency of insects is very frequently, though not always, 

 employed in the fecundation of Orchidea, " but that in those Asclepiadea 

 that have been fully examined, the absolute necessity for their assistance 

 is manifest." 



Aristolochia dematitis, according to Professor Willdenow, is so formed, 

 that the anthers of tliemselves cannot impregnate the stigma; but this 

 important affair is devolved upon a particular species of gnat (^Cecidoviyia 

 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 Jan)es 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 Moncecia, Dicecia, and Polygamia, in which the sta- 

 mens 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 becomes involved in the hair with which in many cases their bodies seem 

 provided for this express purpose, and is conveyed to the germen requiring 

 its fertilizing influence. Sprengel supposes that with this view some plants 

 have particular insects appropriated to them ; as to the dioecious nettle 

 Catheretes urtica, to the toad-flax Cathcrctes gravidas, both minute 

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

 tage in fertilizing the fig which the cultivators of that fruit in the East 

 have long supposed, is doubted by Hasselquist and Oliver^, both compe- 

 tent observers, who have been on the spot.^ Our own gardeners, however, 

 will admit their obligations to bees in setting their cucumbers and melons, 



' Chr. Coar. Sprengel, Entdecktts Gehevnniss, &c. Berlin, 1793, 4to. ; quoted in Ann. of 

 Lot. i. 414. 



* On the Organs and Mode of Fecundation in Orchidcct and Asdepiadece. Linn. Trans. 

 ivi. 731. 



^ Grundriss der Krauterkunde, 353. A writer, however, in the Annual Medical Review (ii. 

 400.) doubts the accuracy of this fact, on the ground that he could never find C. penni- 

 cornis, though A. dematitis has produced fruit two years at Brompton. Bleigen (Dipt. i. 

 100. e.) places this amongst his doubtful Cecidomyia. Fabricius considers it as a Chi- 

 ronomiis. 



* I have frequently observed Dermcstcs flavesrens, Ent. Brit. (Byturus) eat both the petals 

 and stamens of Stellaria holosteum ; and MordcUce will open the anthers with the securiform 

 joints of their palpi to get at the pollen. 



* Hasselquist's Travels, 253. Latr. Hist. Nat. xiii. 204. 



* For a full account of the various opinions on this disputed point, see an interesting 

 article by Mr. Westwood in Trans. Ent. Soc. Land. ii. 214—224. 



