114 BOTANY. [chap. III. 



dominant parasite to surrender a portion of the food 

 elaborated for its own use. 



Amongst the most prominent and general modes of 

 protection of vegetative parts against the attacks of 

 living enemies may be mentioned prickles, as in roses 

 and brambles, which may either be straight, and thus 

 prevent 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 

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

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

 tum officinale). Stinging hairs, as in the common nettles 

 {Zfrtica dioica, and U. urens), in these cases the stinging 

 hairs are mixed on the leaves and stem with ordinary 

 rigid hairs, of which they are higher developments, dis- 

 tinguished by the lower or basal swollen portion 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 wormwood {Arte- 

 misia vulgaris), chamomile {Anthemis nobilis) , and the 

 leaves and fruit of the walnut {Juglans regia). Poisonous 

 alkaloids, as in the species of Strychnos, which contain 

 ,two very poisonous alkaloids, strychnine 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 nux-vomica, are valuable medicines, depend- 

 ing 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 



