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.2 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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