Minnesota Plant Life. 507 



in short, so much Hke stones that they are hkely to be passed 

 over as members of the mineral kingdom. Such an appear- 

 ance must help them just as its green color helps the tree-toad 

 by making it inconspicuous. Another kind of mimicry has 

 been thought to characterize certain tropical herbs with mottled 

 leaves. Some begonias and aroids suggest themselves as ex- 

 amples. It has been supposed that by their resemblance to 

 snakes they may avert danger to themselves, from grazing 

 animals. The sensitive plant, which at a slight shock drops 

 into an apparently shriveled and dry condition, may by this 

 behavior startle or deceive animals that would otherwise feed 

 upon its foliage. 



Utilization of allies is a not uncommon method of defense. 

 Thus, plants growing in hedge-rows obtain protection because 

 the thorny or impenetrable vegetation about them is sufficient 

 to withstand the attack of animals. Some plants may obtain 

 defense by hiding themselves in out of the way places, but this 

 is scarcely a calculable matter. A peculiar alliance is that 

 which exists in the tropics between certain trees and ants. In 

 these regions leaf-cutting ants are abundant and some trees, by 

 the secretion of sweet liquid on the twigs, attract large num- 

 bers of warrior ants that feed upon the honey. The plants even 

 develop shelter for such ants and when leaf-cutting ants attempt 

 to ascend the tree the honey-eaters swarm out and ofifer battle. 

 An ant-defended tree, such as a Cccropia, is an extraordinary 

 object. A slight blow upon the trunk calls out thousands of 

 angry ants from every crevice. By keeping such a body-guard 

 of insects, the plant undoubtedly protects itself. ]\Iany other 

 such alliances might be mentioned but one further example 

 must suf^ce. 



Seedlings of trees are particularly exposed to harm. As in 

 man, so in plants, the expectation of life is at first decidedly 

 low. Most seedlings perish before they are firmly established 

 and those that are fortunate enough to persist and finally to 

 mature into sapling-trees have generally been nursed along b\ 

 surrounding plants which have happened to be of kinds not un- 

 favorable to the seedling itself. Thus the young red pine 

 plants make excellent nurses for the seedling of the white pine, 

 and if the former are abundant on the forest floor, the white 

 pines are more likely to obtain a foothold. 



