Apr., 1922] RAINES- VEGETATIVE VIGOR OF THE HOST IQ5 



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 parasites. 



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. 



