INSECTS IN RELATION TO PLANTS. 551 



in which, as in Ricinus, the female parts are above the male ones, can 

 therefore be only thus impregnated. The same in the whole family 

 of orchideous plants, in which indeed the anthers are placed above the 

 stigma, but frequently consist of a viscid waxy mass, whence the pollen, 

 upon the shaking of the plant, cannot fall upon the stigma, but only 

 by means of insects which visit the plant, and who smear themselves 

 with this clammy substance, can it be rubbed upon the stigma. The 

 Aristolochia clematitis, in which there is also observed a growing 

 together of the filaments with the style, is impregnated by a little fly 

 peculiar to it, the Tipula pennicortiis, Lin., and which belongs to 

 Meigen's genus Ceralopogon. This little creature creeps through the 

 tubular portion of the flower into the lower cavity where the nectaries 

 are placed, but cannot return back, hairs placed in that direction pre- 

 venting it. Whilst it now flutters about for several days until the 

 flower fades, it brings the pollen into contact with the stigma, and thus 

 causes impregnation. It appears also that other plants require certain 

 species of insects to facilitate their impregnation ; and it may originate 

 thence that so many exotic, and especially tropical, plants, produce no 

 seed in our hot-houses, as they have not the peculiar insects requisite 

 to promote it. This appears to be confirmed by the observations 

 made upon indigenous plants, namely, upon Nigella arvensis, Iris 

 xipliium, and the species of Antirrhinum, that they are also visited 

 by insects of only one species or of one genus, and therefore more 

 frequently remain unproductive than others to which many insects 

 resort, as the Umbellala, Syngenistce, &c. Many insects, namely, bees 

 which live solitary, and especially the males, pass the night also in 

 flowers, for instance, Chelostoma truncornm, Labr., which reposes in 

 the large Campanulas with pendent flowers. In these visits they like- 

 wise must bring the pollen into contact with the stigma. The 

 Syngenistce, in which the stigma in general projects far above the 

 coronet of anthers, are visited by innumerable small beetles, particularly 

 Nilidula aenea and the Thripes, which creep down into the recesses of 

 the flower, and naturally upon their return touch the stigma with their 

 body covered over with pollen, whence arises, as we have before 

 remarked, the great fertility of these flowers. 



These remarks may suffice as a proof of the reciprocal relation 

 between plants and insects. A more detailed account of it may be 

 found in the book that we have before referred to of Ch. K. Sprengel. 



