52 THE SURVIVAL OF THE UNLIKE. [l. 



vent the nibblings of animals, or in more advanced 

 species, curved, thus enabling the weak stem to climb 

 and carry its leaves out of harm's way. Spines, that are 

 sharp -pointed abortive branches, serving the same pur- 

 pose as prickles, as in the common sloe or blackthorn 

 {Prumis spinosa). Rigid hairs on leaves and stem, as 

 in the borage {Borago officinalis), and comfrey {Sym- 

 phytum officinale). Stinging hairs, as in the common 

 nettles {Urtica dioica, and JJ. urens) ; in these cases the 

 stinging hairs are mixed on the leaves and stem with 

 ordinary rigid hairs, of which they are higher develop- 

 ments, distinguished by the lower or basal swollen por- 

 tion of the hair containing an irritating liquid that is 

 ejected when the tip of the hair is broken off. Bitter 

 taste, often accompanied by a strong scent, as in worm- 

 wood {Artemisia vulgaris), chamomile {Anthemis no- 

 hilis) , and the leaves and fruit of the walnut {Juglans 

 regia) . Poisonous alkaloids, as in the species of Strych- 

 nos, which contain two very poisonous alkaloids, strych- 

 nine and brucine, in the root and the seeds; decoctions 

 of species of strychnos are used by the Javanese and the 

 natives of South America to poison their arrows. Some 

 of the species, as Strychnos mix- vomica, are valuable 

 medicines, depending on the strychnine they contain, 

 which acts as a powerful excitant of the spinal cord and 

 nerves; thus the most effective protective arrangements 

 evolved by plants can be turned to account, and con- 

 sequently lead to the destruction of the individuals 

 they were designed to protect. Our common arum 

 {Arum maculatum), popularly known as 'Lords and 

 Ladies,' has an intensely acrid substance present in the 

 leaves, which effectually protects it from the attacks 

 of mammals and caterpillars, but not from the attacks 



