On Evil in Small Doses 
So also with the thickening of the epidermis walls 
when a plant is exposed for the first time to desert con- 
ditions ; particle after particle of protoplasm is, so to 
speak, “hurried to the front,” and there secretes itself 
into cellulose until the outer wall, the first line of defence, 
is so thick that no harm can arise to the live protoplasm 
within. But it is upon the method of, and resistances 
to fungus attacks, that we have the most valuable of 
recent researches. 
The first effect is to stimulate the living protoplasm 
of the leaf cells, It has been found by direct testing that 
the amount of enzymes is greatly increased. In diseased 
mulberry leaves there are more diastases, invertases, and 
oxydases than under ordinary circumstances.*® One 
can realise what is going on in such cases from the vivid 
account given by Miss Gibson of one of her experiments, 
A rust-spore (Uredo chrysanthemi) was placed upon 
the leaf of a chrysanthemum. The spore put out its 
tiny but deadly germ-tube, which felt its way to a stoma 
and then grew down, through the opening, into the 
leaf. Then the battle between the secretions of the 
fungus and the counter-secretions of the leaf cells con- 
tinued for four days. But the leaf conquered, for the 
fungus-tube withered and died. Yet it was not won 
without some loss, for a circle of dead leaf cells marked 
the battlefield. 
Mr. Salmon actually interfered in a struggle of this 
kind, and with disastrous results, so far as the plant was 
concerned, There are certain mildews (Erysiphe) 
which attack the leaves of Brome-grasses. He found by 
experiment that one of these mildews was unable to 
attack a particular Bromus. Then he began to help 
the fungus, He sliced a very tiny piece of the surface 
away from the under side of a leaf. This depressed its 
vitality and it succumbed to the attack, Even a slight 
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