INDIRECT BENEFITS DERIVED FROM INSECTS. 293 



knowingly fulfill the intentions of nature in another de- 

 partment a . 



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 si- 

 tuated on the upper side of a transverse membrane (a rats 

 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 improperly regarded as 

 fulfilling the office of a stigma, Now as the anther is situ- 

 ated at the base of the style-flag which covers it, at a con- 

 siderable distance from the stigma, and at the same time 

 cut off from all access to it, by the intervening barrier 

 formed by the circus eminens, it is clear that but for some ex- 

 traneous agency the pollen could never possibly arrive at 

 the place of its destination. In this case the humble-bee is 

 the operator. Led by instinct, or, as the ingenious Sprengel 

 supposes, by one of those honey marks (Saftmaal) or spots 

 of a different colour from the rest of the corolla, which, ac- 

 cording to him, are placed in many flowers expressly to 

 guide insects to the nectaries, she pushes herself between 

 the stiff style-flag and elastic petal, which last, while she 

 is in the interior, presses her close to the anther, and thus 

 causes her to brush off the pollen with her hairy back, 

 which ultimately, though not at once, conveys it to the 

 stigma. Having exhausted the nectar she retreats back- 

 wards ; and in doing this, is indeed pressed by the petal to 

 the circus eminens ; but it is only to its lower or negative 

 surface, which cannot influence impregnation. She now 

 takes her way to the second petal, and insinuating her- 

 self under its style-flag, her back comes into close contact 

 a Smith's Tracts, Kid. Kolreuter, Ann. of Bol. ii. 9, 



