UNDESIRABILITY OF UNBIDDEN GUESTS. 



231 



new and fresh. Winged insects and humming-birds are ideal agents for the crossing 

 of flowers, and are the most welcomed of all guests. But even of these fleet 

 emissaries all are not equally welcome. Of what service is it to a plant if its 

 pollen is not deposited on the proper spot on the stigma where it can develop 

 pollen-tubesbe the transfer accomplished ever so quickly? Let us suppose a tiny 

 fly entering the flower of a Foxglove. It alights on the lower lip of the corolla and 

 makes its way to the honey at the base of the flower where the honey is, without 



Fig. 260. Cornusflorida; numerous small, aggregated flowers surrounded by four huge bracts, which serve at once as 

 attractive-organs and alighting-platforms for insects. (After Baillon.) 



touching the stigma or stamens placed just below the upper lip. Having satisfied 

 itself, it retreats by the same route. What advantage does the flower get from the 

 visit of this particular insect ? None. And more than this, it has been robbed of a 

 portion of that honey on which it relied to allure some larger animal which would 

 unintentionally stroke the anthers and stigma with its body. By the admission 

 of small flies to Foxglove flowers consequently no transfer of pollen would be 

 effected. Thus we see that not all flying animals are desirable visitants; that many 

 insects, which, in consequence of their size and shape are unable to promote a 

 transfer of pollen, must be regarded as unbidden guests, and prevented access to the 

 honey. 



Nor are arrangements such as are indicated above wanting. Peculiar folds and 



