Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 
Stakman (1914, p. 15) increased the susceptibility of cereals to rusts 
to which they are ordinarily highly resistant by slight anaesthetization with 
ether and chloroform. Jost (1907, p. 195) states that weak etherization 
accelerates respiration, and such treatment is usually considered as stimulat- 
ing the metabolism of the plant. Stakman (1914, p. 39) also describes an 
experiment in which it was sought to influence the susceptibility of wheat 
plants grown in water cultures by introducing various salts into the culture 
solution. Copper sulphate, copper carbonate, and iron sulphate were 
added in varying amounts. The results showed that none of the salts ex- 
perimented with appreciably decreased the amount of rust when used in 
such concentration as to permit the normal development of the host plant. 
Infection was secured on all the plants, even those which were stunted to 
one sixth their normal size. 
Eriksson and Hammarlund (1914) report partial success in delaying 
and inhibiting the development of Puccinia malvacearum on Althea rosea 
by treating the soil with a 3 to 5 percent solution of copper sulphate. They 
give no data on the vigor of the plants. 
Bailey (1920, p. 76) found that hollyhock plants stunted by red spider 
showed comparative immunity to rust. 
Trauma 
There are only two recorded experiments on the effect of trauma on 
susceptibility to rust; they do not agree in their findings. Trauma usually 
has an immediately stimulating effect on the metabolism of a plant tissue 
and might be expected to increase susceptibility to rust. Hecke (1915) 
mentions that Barfuss working in his laboratory has demonstrated that 
wheat rust, which ordinarily does not go to rye or barley, readily infects 
rye and barley leaves if they have previously been injured. After cultivat- 
ing the rust for seven generations on wounded leaves, Barfuss succeeded in 
definitely obtaining infections on uninjured leaves; but these did not mature 
spores. The rust did not lose its power to go back to wheat. This is much 
after the manner of Salmon's work in increasing the susceptibility of re- 
sistant host plants to Erysiphaceous paravsites. 
Similar efforts to these by Stakman, also working with cereal rusts, 
gave negative results. Stakman (1914, p. 16) found leaf injury to have no 
effect on susceptibility to rust. 
In one experiment 16 leaves were pricked full of holes in an area of one centimeter or 
more. They were then inoculated and 4 became flecked, but no pustules developed. 
Histological examination showed that the spores had sent out germ tubes in large numbers. 
These grew among the host cells, but true infection did not take place. Sections of these 
plants were made and examined. It was clearly evident that leaf injury did not increase 
the chances for infection. 
