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. 
