On Evil in Small Doses 



of cork on injured stems, and the great and unusual 

 flow of resin whenever certain Coniferae are wounded, 

 show a distinct effort of the plant which must surely be 

 the result of a stimulation of its life-processes. When 

 the balsam fir (Abies balsamea) is attacked by a rust- 

 fungus, it also responds by increased resin flow and by 

 forming a larger number of bud-scales than usual. 17 



Nor is it only the flowering plants which show the 

 power of dealing adequately with an emergency of this 

 kind. 18 Polyporus and Coprinus, when their sclerotia 

 are injured, are able to form a new brown protecting 

 envelope. 



All these and many other instances show that evil in 

 small doses is often a strong stimulus, which somehow 

 calls into existence adequate remedies. 



It is only by its strange power of secreting some 

 appropriate substance that vegetable protoplasm can 

 deal with such situations. 



Of this power there are many remarkable instances. 

 In the life of a palm leaf, for instance, there comes a 

 time when the old and dead leaf is a nuisance rather 

 than a help to the tree. Then one finds remarkable 

 modifications going on near the base of the leaf-stalk. 

 First a continuous group of cells, across its base and at 

 an angle of 45 degrees to it, deposit cork in their walls ; 

 then, beyond these, the walls of the neighbouring cells 

 degenerate into some jelly-like modification of cellulose. 

 When wet weather comes, this gelatinous material swells 

 so that the cells become spherical, and in consequence 

 the great leaf drops gently and softly away, leaving a 

 well-corked scar by which no fungus can enter. 19 



The whole of this complex procedure has been 

 arranged simply by the secretion of cork and the change 

 of cellulose into its gelatinous variety in one part of the 

 stalk 1 



332 



