40 THE HUMAN SIDE OF PLANTS 



lured him to destruction. It is reasonable to sup- 

 pose that in the distant future some of these plants 

 which win their prey by means of viscid hairs or 

 surfaces will develop into insect-eating plants, as 

 the sundew, Venus's fly-catcher, the pitcher-plants, 

 and one of the bladderworts have done. Darwin 

 believed that many plants, such as the saxifrages, 

 not classed with insect-eaters, actually get some 

 food from the trapped insects. 



But the mere fact that a plant catches insects is no 

 proof of its carnivorous nature. Numerous plants 

 have their leaves and stems covered with sticky 

 hairs, which continually catch insects ; and yet, they 

 show not the slightest tendency to absorb or digest 

 the food thus captured. The stems and leaves 

 of the rhododendron, some species of solanum, and 

 the stinking groundsel, all use this method of trap- 

 ping unwelcome visitors. 



An interesting evidence of the discretionary pow- 

 ers of these plants is the fact that when cold 

 weather drives away or kills the crawling insect 

 life, this stickiness ceases. The need no longer 

 exists, and the supply dries up. In the same way, 

 the gummy fluid on the scales which enfold the 

 leaf -buds of the horse-chestnut and the balsam 

 poplar, in the springtime, disappears when no 

 longer needed. 



