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tity of acid in seeds (see Tab. 2, 3, pp. 76— 77), but these differences are-

only correlative with the immunity of plants and do not explain tire nature

of their immunity.

K i r c h n e r ’ s analysis of six varieties o f wheat (1916) to prove

the acid theory ol immunity is not persuasive, being, if at all, convincing

only in relation to yellow leaf rust

(Puccinia glumamm)

, but not to the

infection of the same varieties by brown rust

(P . triticina).

3. It is impossible to connect the principle of C o m e s with the

high specialisation of parasitic fungi in their choice of host-plants. To sup

pose that all tire difference of host-species and genera, recognisable by the

parasites consist in the quantitative difference in organic acids in their

cell-sap is evidently not correct and cannot be proved.

The connection of immunity with the anlocian pigments, also indi

cated by C o m e s , is not persuasive as there are many exceptions, perhaps

more exceptions than positive data.

The C o m e s ’ theory of «ingentilimento» of cultivated plants

compared with their wild progenitors having as a result their greater sus

ceptibility, is not persuasive, as many of the wild «progenitors» are not

less susceptible than the cultivated forms. E. g.

Linurn angustifolium, A vena

falua

Triticum dicoccoides, Arena Ludoviciana, Hordeum sponianeum,

etc.

M a r s h a l l W a r d supposed that as a result of inoculation, the

immune varieties form special substances «antitoxines» which paralise the

parasite's action, as it is proved in the animal kingdom. But this analogy

is only a supposition, the correctness of which has yet to be proved. Till

now we know almost nothing of plant antitoxines.

In general neither of these theories of physiological immunity, in the

opinion of the author can explain the various phenomena of immunity.

As a matter of fact it is evident that physiological immunity depends on

very complicated physiological inter-relations between the protoplasm

of the host-cells and the parasite. Phenomena of susceptibility are often

connected with the phenomenon of symbiosis. The individuality of the

parasite has also a great influence, moreover, the same parasite might act

differently on the same host-plant at its different stages of development.

Many varieties of

Asparagus

for instance are immune to

Puccinia asparagi

D. C. at the stage of uredospores and no noticeable varietal difference exist

in relation to the accidio stage.

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