ЭлБиб

Plants resistant to’ fungus. Scattered small single pustules on leaves

surrounded by distinctive yellow spots. A part of the pustules is unable to

force its way through the epidermis.

Plants very resistant. Very few small single pustules surrounded by

yellow spots, many of which cannot break the epidermis and yellow or

brown spots only show the traces of infection.

Plants quite immune. No pustules of fungus at all.

For other fungous diseases as well as for bacterial diseases this scale

should be correspondingly changed.

1' Tn' ordebto give a concrete representation of the extension of the pheno

mena of immunity among varieties of plants, the author gives a summary

of data on the distribution of immunity to infectious diseases among culti

vated plants according to the investigations of diffrent authors, as well ns

from his own observations.

Data arc given for wheat, barley, oats, rye, millet, maize, rice, flax,

cotton, potatoes, beet-root, cabbage,.tobacco, clover, sunflowers, asparagus,

beans, gooseberries, vines, apple and pear-trees, roses and hops in relation

to their chief fungous and bacterial diseases (pp. 18—39).

, These data show clearly that the. phenomena of immunity are broadly

distributed among the most different families of

Alonocoliledonae

and

I)ic&~

tiledonae

and manifest themselves in relation to different genera of fungi

from

Basidiomycetes

and

Ascomycetes

Bacteria.

The phenomena of immu

nity are manifest also in relation to the higher parasites, as for instance in

sunflowers to

Orobanchc

and in other plants to

Crmula.

The essential fact manifested by these data is that there exist many

varieties immune to one parasitic fungus, while at the same time there are

no varieties immune to another fungus, or only a very few. E. g. in roses—

hundreds of varieties are immune to rust and mildew

( Pliaragmidium subcor-

ticium and Sphere theca pannesa).

Whole polimorlous species like

Triiiaim

durum

;

T. monococcum,' T. turgidum

and

T. polonicum

are immune to brown

rust

(Puccinia irilicina),

still more—half of all existing varieties of

wheat are more or less immune to yellow rust

(P . glumarum)

. There are at

the same time very few varieties immune to smuts,1— in several plants, like

millet

(Panicum milliaceum)

, there arc no immune varieties at all. Even

in relation to morphologically nearly allied species of fungi we observe

quite different relations of host-varieties. E. g. there exist many varieties

of oats immune to crown rust

(P . coronifera)

but only two of 450 varieties

tested by the author have proved to be immune in a small degree to black

rust

(P . graminis).

The explanation of the difference in the relation of the same varieties

to different fungi, which is of great importance to plant-breeders, is

given in the 4-th chapter.

Научная электронная библиотека ЦНСХБ