128 SAGACITY AND MORALITY OF PLANTS. 



bark of trees, it is by no means limited to that 

 portion. Its presence there can be easily understood, 

 for if the bark were gnawed all round by ruminating 

 animals (as they have a tendency to), the tree would 

 be destroyed. It is between the protective bark, 

 and the woody stem, that each year's layer of annular 

 growth is formed. An extra secretion of tannin 

 in the bark, therefore, must be highly protective ; 

 and how much is formed there is indicated by the 

 fact that our commercial supplies are derived chiefly 

 from the bark of trees alone. 



Tannin, however, is found in its most concentrated 

 state in certain fruits, such as the acorn, walnut, 

 beechnut. It forms in the dark-brown skin, which 

 all eaters of walnuts are careful to peel away before 

 partaking of the white flesh ; although they may not 

 be aware that this part, defending like an inner wall 

 after the hard shell has been broken through, is the 

 counterpart of that other inner defence, known as the 

 " stone " {endocarfi)^ found in such pulpy fruits as the 

 plum ; whilst the hard shell, and, in the case of the 

 acorn the tough and leathery outer skin, is the 

 equivalent to the outer layer of succulent and juicy 

 flesh, for whose sake the plum is cultivated. 



Tannin is more or less abundant (and its presence 

 must always be explained on the ground of its being 

 a defence against various enemies), in the Oak, Elm, 

 Willow, Elder, Plum, Cherry, Sycamore, Birch, Poplar, 

 Hazel, Ash, etc., the three first possessing it perhaps 



