94 ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



brushes and thickets of hairs are present, guarding the entrance 

 and rendering access difficult, whilst still allowing it. Large 

 and powerful animals find these obstacles no hindrance, and 

 readily brush them aside; small ones, however, cannot do this, 

 but have to climb over or circumvent the obstacles. And in 

 many cases this enforced divergence by small insects from the 

 direct path brings about the desired result. For, in circumventing 

 these folds and barricades and hairs, they are unconsciously led 

 past the anthers and stigmas, contact with which is unavoidable. 

 Thus, what would otherwise be useless visitants become welcome 



guests. They are conducted indirectly 

 to the honey by these curious struc- 

 tures, which may, in a sense, be termed 

 "path-finders'." Cursory examination 

 of such flowers as Foxglove or Pansy 

 will show the presence of barricades 

 of the kind mentioned (see also fig. 

 1085). Path-finders for the guidance 

 of invited guests are often present in 

 the form of conspicuous colour-streaks, 

 which converge towards the source 

 through Flower of a of nectar. Pansy, Azalea, and Pelar- 

 Sh wing g nium are Particularly good examples 



of this. 



The defences and other arrangements which have been evolved 

 in various connections by plants and animals are never completely 

 successful, and with changed surroundings are apt to fail. This 

 applies not only to " mice and men ", but also to flowers. Kerner 

 states, for example, that the flow T ers of some 300 European plants 

 are systematically robbed by humble-bees, which take a short cut 

 to the nectar by biting through the calyx or corolla. The result 

 may be disastrous, for in some of these plants but few seeds are 

 produced, so that they are becoming rare, and in course of time 

 will probably die out altogether. Certain Alpine Catch- Flies (Silene 

 Pumilio and ,S. Elizabeths) are in this evil case. Kerner suggests 

 that such plants date back to a time when there were no, or but 

 few, humble-bees in the region where they now grow, and that they 

 have since failed to evolve means of defence against the new kind 

 of attack. 



Wingless enemies of soft-bodied character, especially snails 



