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on the contrary that Pb(N03)a and Zn (N03)a increase its susceptibility.

The methods of the observations were not irreproachable (175). The

author repeated these experiments with a number of controls and artificial

equable infection of plants. The data and photos of these experiments

are given in Tables 9, 10, 11, 12 (pp. 105— 108). These data state the

following:

1) That immune varieties keep their immunity even under the influence

of salts like Zn(N03)a and РЬ(Ж)3)г, which are known, to increase the

susceptibility of plants to infectious diseases ( S p i n k s ) .

2) That the susceptibility of wheat to mildew may de diminished in

a smaller degree,at least in the first stages of vegetation and indefinite

conditions (in this case, by putting different Li salts into soil, but not

into manured sand),under the influence of the salts of Li.

. The physiological nature of this influence of Li salts on the suscepti

bility of wheat is not clear, the more so because it lias, been noticeable

only in soil culture, where it is very difficult to distinguish the role of se

parate factors, due to complicacy ol environment (absorption, etc.).

Without generalising this experiment (against a broad generalisation

of which are the results of other experiments as well as the above data)

this experiment, nevertheless, confirming S p i n k s ’ observations /states that

the, susceptibility of the plant: to the parasite might be diminished in some

cases under the influ: nee of environment and therefore we cannot deny, in

principle the possibility of chemical action of substrate on physiological

immunity. ..

The possibility of . changing the physiological immunity through the

influence of environment is not excluded on account of its dependence in

some cases on the age of the plant.

... As to the dependence of immunity on such factors as temperature,

light and humidity there are n> definite experimental data and it is extre

mely difficult to separate the influence of these factors on plants from

direct action on parasites themselves.

On the whole all the facts given above point to the slight changeable

ness of physiological immunity under the influence of environment. In

this direction the immunity of animals to bacterial diseases is much more

variable (see Pasteur’s experiments with poultry in relation to antrax.

Ernst’s experiments with frogs, Behring’s experiments with white mice).

It is not unlikely that the greater plasticity of immunity of animals is

connected -with feebler specialisation of many infectious bacteria. On the

contrary the greater independence of physiological immunity of plants is

dependant on the specific character of parasites and hosts. And specific

qualities of organisms depend very little on environment, as is evident

from the experiments of transplantation;

"’ E. F i s c h e r and G. S a h 1 i (52, 157) proved the above experi

mentally in the case of physiological immunity by grafting immune spe

cies to susceptible ones and infecting so called «chimeras»

( Cralaegomei-

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