Arrangements for Securing Union of Sexes 325 



"unbidden guests," as Kerner so happily called them. In one 

 instance, at least, plants seem quite helpless against such an 

 attack, for Bees often puncture the nectariferous spurs of Colum- 

 bines and Larkspurs in our gardens without entering the flower at 

 all; but this is exceptional, and 

 presumably a recently-acquired 

 habit of those insects. A partial 

 protection against unbidden guests 

 is secured by the adaptation of 

 floral to insect shapes already de- 

 scribed, in correlation with which 

 most insects visit only the flowers 

 to which they are fitted, leaving 

 the others alone. But there is one 

 kind of insect, whose small size 

 and other characteristics make it 

 useless as a cross pollinator, but 

 which is at the same time a par- 

 ticularly pertinacious nectar lover, and that is the Ant, against 

 which, accordingly, especial protection is needed. A number 

 of adaptions preventive of its access to nectar appear to 

 exist. Possibly the extra-floral nectaries earlier described 

 (page 212), may provide a bait to keep these insects from 

 the flowers. Furthermore this is probably the explanation of 

 the closure of the throats of flowers, best exemplified in the 

 Snapdragon, in a way to open by the pressure of a large insect's 

 weight or strength but not to the small body of an ant ; while the 

 rings of scales or hairs in the throat or somewhere in the tube of 

 the flower (figure 119), or sticky glands all over the outside of the 

 calyx or neighboring parts (figure 120), have probably the same 

 explanation, as have a number of other arrangements of minor 

 account described by Kerner in his charming book devoted to the 

 subject. 



It is thus plain that flowers, hke other parts of the plant, are 



Fig. 119. — Interior of a flower of Coboea 

 scandens, showing the masses of hairs 

 commonly believed to protect the 

 nectar from insects unadapted to ef- 

 fect cross pollination. (Copied from 

 Kerner's Pflanzenlehen.) 



