On Evil in Small Doses 



The researches of Klebs * have shown that it is possible 

 to do this at least in some particular cases, and they 

 have, in consequence, an extreme importance which has 

 not yet been realised by practical breeders. 



When a vegetable is exposed to a dangerous crisis, 

 which happens continually, it always tries to resist and 

 defend itself. 



Suppose a hungry and thirsty root to be growing in 

 a stubborn sand composed, let us say, of aluminium, 

 silicates, and such like refractory material, then the very 

 extremity in which it finds itself causes the root to respire 

 harder, that is, to take in more oxygen and give out more 

 carbonic acid. But this very carbonic acid given off is, 

 in water, a powerful solvent, and will attack those flinty 

 particles and furnish more food material to the root. 



Fungi seems to be even more efficient in dealing with 

 stubborn soils than ordinary root-hairs, as, for instance, 

 those lichens which attack granite or even quartz. The 

 common mould-fungi are able to excrete not only car- 

 bonic acid, but malic, tartaric, formic, and lactic acids. 

 This formidable array of assisting acids helps them to 

 corrode granite, basalt, and even quartz sands.^ These 

 secretions will surely be increased by the stimulus of 

 hunger, just as happens with the ordinary respiration of 

 roots (see below). 



The effect of salt upon the living protoplasm of sea- 

 side plants has already been mentioned. Common salt 

 is a deadly poison when in excess, yet several plants have 

 not only trained themselves to live on salt-banks but 

 do not seem, at first, to be quite comfortable when their 

 customary poison is removed, for Salicornia seedlings are 

 said to germinate better in salt than in fresh water. 



It has been found that several very poisonous mineral 

 salts, when given in minute doses, stimulate the growth 

 of certain fungi. This holds true of zinc sulphate and 



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