3o6 THE BIOLOGY OF FLOWERING PLANTS 



the old leaves die slowly and are cast off. Robbed of its 

 anchors, the smooth stem slips down by its own weight, 

 till the upper lashes are again fast. At the foot of the tree 

 lies, in great coils and loops, the sunken part of the stem 

 as thick as a man's arm. ... In the forest this mighty 

 cable may reach the length of 200 to 300 metres." 



II. Protection against Animals and against Other 



Plants 



It is the general fate of the plant to serve as food for the 

 animal, but, for life on earth to be possible, a certain balance 

 must exist. Nor does the plant, except in the cases where 

 seed distribution is involved, benefit by being devoured. 

 It is common for plants to show features which protect them 

 against the ravage of this animal or that. Every plant is 

 not easy food for any animal. Protection against rodents 

 and ruminants by means of sharp thorns and spines is an 

 obvious case, and its obviousness has led to the acceptance 

 of this and other devices as protective without very much 

 experimental evidence. In a work of Stahl's (1888) we 

 have, however, a monograph which deals very carefully 

 with one aspect of the problem, and also refers to more 

 general questions. A treatment of the subject is also given 

 by Kerner and by Neger. 



Stahl points out that the protection of a plant is usually 

 only partial, against some few animals ; but that this may 

 yet be of extreme importance, for one enemy more or less 

 may make all the difference between extinction and survival. 

 He gives as an instance the decimation of the European 

 vine by the Phylloxera introduced from America, a pest 

 unable to do serious damage to the roots of the American 

 species. Plants which are avoided by most animals may be 

 the favourite food of one or a few. Thus Euphorbia 

 Cyparissias, the cypress spurge, is never touched by 

 ruminants, rodents, snails, or grasshoppers, but is the only 

 food of the caterpillar of the moth Sphinx euphorhice. The 



