THE AMERICAN BOTANIST. 



81 



for his health. From this it appears that we cannot pro- 

 nounce upon the utiHty of an\^ plant structure considered 



solely from mankind's standpoint. 



* * 

 * 



Scientists are accustomed to account for any special 

 features of plants upon the theory of evolution. Thus 

 spines, thorns and prickles are supposed to protect their 

 possessors from animals that would otherwise devour 

 them. The ferns, however, strongly contradict this, for 

 the tree ferns of the tropics, with great coarse fronds high 

 in air have their trunks thickly set with sharp thorns, 

 while the tender herbaceous species on the earth have no 

 such protection. Possibly the spines and prickles of the 

 cactus protect its succulent body from thirsty herbivores, 

 but if one examines the vegetation in its vicinity it will be 

 found that other plants have similar armor though they 

 would scarcely tempt a browsing animal if guiltless of 

 such defenses. Is the foliage of the rose so tempting that 

 it requires prickles to defend it, while its cousin, the spi- 

 raea fights life's battles unarmed ? The more we study 

 facts of this kind the more certain it appears that many 

 plant structures once thought necessary to the plant's 

 success in the struggle for existence, are more properly 

 considered as matters by the way. 



* 



The same is undoubtedly true of plant-secretions. 

 Starch and similar elements are stored up by plants for 

 themselves or for their seedlings, but there are other sub- 

 stances that plants produce only to get rid of. In manu- 

 facturing elements for their own use, various by-products 

 are thrown off that are useless. In the partridge-pea and 

 the bracken we may find these products excreted through 

 glands. Other plants, lacking glands, store them up in 

 their tissues. That these secretions are often harmful to 

 the plant is shown by the fact that quinine will poison the 

 Cinchona tree that produces it, and aconite and bella- 

 donna have similar effects upon the plants from which 

 they are obtained. 



