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guishos itself from susceptible varieties of this species by an absolute immu

nity to mildew.

In general, as a rule, a marked immunity of a variety is connected

witli a distinctive genetical place among other varieties.

This regularity is quite clear for groups distinctly differentiated and

thoroughly studied genetically. For groups, polymorphous but nearly allied,

this regularity, of course might not be so evident1).

The same regularity can he seen in other plants. The relation of diffe

rent varieties of roses for instance, coincides with their genetical diffe

rentiation. American vines, genetically quite distinct from European vines,

arc correspondingly immune to many specialised parasites, as

PJasmopara

cilkola. Uncinula neca/or, Manginia ampeh'na.

etc.

From the above a new kind of regularity results, namely the con

nection of reactions of the same varieties to different parasites. The most

accepted view that a variety .immune to one parasite,is as a rule susceptible

to another is not correct.

On the contrary the relation of the same varieties

lo equally specialised

parasites

is very often similar. The accepted view is correct only in relation

of varieties to differently specialised fungi, i. e. to narrowly specialised

and feebly specialised parasites.

The Tables give many examples of such a connection of reactions.

As a matter of fact all durum wheats and engrains are chatacterised simulta

neously by immunity to yellow rust, brown rust and mildew. •

T. dicoccum

which consists of two groups of varieties in relation to

brown rust: one immune, another susceptible,is divided correspondingly

in relation to yellow rust and mildew. Moreover,there is a definite connection

of immunity to brown rust, yellow rust,and black rust

(P . graminis).

Varie

ties most resistant to black rust are among varieties immune to brown

riisl and mildew.

Yellow rust of wheat is more sensitive as to varietal differences. Very

often varieties susceptible to brown rust are characterised by immunity to

yellow rust. But in general, all varieties immune to brown rust, mildew

and black rust,are immune also to yellow rust.

In oats, as Tables show, this connection is even more clear. A variety

strongly immune to crown rust is usually comparatively resistant to mildew.

') Among other parasitic fungi of wheal Puccinia glumarum f. tritici—yellow

rust is more sensible to varietal differences. Even nearly allied varieties of T. vulgare

and compactum show in some cases sharp differences in their susceptibility to this

rust.

Eriksson and Henning's conclusion (Getreiderosle p. 340) that there is no conne

ction of immunity of vari'ttos to yellow rust with their genetical place is not correct.

In fact, it is not quite clear in relation to nearly allied varieties of T. vulgare and T. com

pactum (e. g. varieties of square-head), the* phytogeny of which we know but little.

Rut, on the whole even to this rust the relation of species and distinct genetical groups

of wheat (see Tables) shows a definite regularity in parallelism of phytogeny of varieties

with their immunity.

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