294 INDIRECT BENEFITS DERIVED FROM INSECTS. 



with the true stigma, which is thus impregnated with the 

 pollen of the first visited anther : and in this manner mi- 

 sTatins- from one part of the corolla to another, and from 

 flower to flower, she fructifies one with pollen gathered 

 in her search alter honey in another. — Mr. Sprengel 

 found, that not only are insects indispensable in fructify- 

 ing the different species of Iris, but that some of them, as 

 I. Xiphium, require the agency of the larger humble-bees, 

 which alone are strong enough to force their way beneath 

 the style-flag : and hence, as these insects are not so com- 

 mon as many others, this Iris is often barren, or bears im- 

 perfect seeds a . 



Aristolochia Clematitis, according to Professor Willde- 

 now, is so formed, that the anthers of themselves cannot 

 impregnate the stigma ; but this important affair is devol- 

 ved upon a particular species of Tipula ( T. jpennicomis). 

 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 in- 

 sects 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 intrusted to them is completed, and impregna- 

 tion 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 pri- 

 son b . Sir James Smith supposes that it is for want of some 



a Chr. Conr. Sprengel Entdecktes Geheimniss, $c. Berlin 1793, 

 4to. quoted in Ann. ofBot. \. 414. 



b Grundriss der Krduterkunde, 353. A writer however in the An- 

 nual Medical Review (ii. 400.) doubts the accuracy of this fact, on the 

 ground that he could never find T. pennicornis, though A. Clematitis 

 ha? produced fruit two years at Bromptcn, 



