Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 189 
green-leaved pink known to be very susceptible to carnation rust, and they 
were grown in five different soils ranging in composition from one that was 
principally sand to one containing chiefly organic matter. Sheldon's ob- 
servations indicated that the growth of the host varied directly with the 
amount of organic matter, nitrogen, and silt in the different soils; and that 
with increased vigor and growth of the host the incubation period of the 
fungus decreased in length, from 21 days in the poorest plants to 16 days 
in the most vigorous individuals. 
Miss Gibson (1904, p. 188) describes an experiment on the effects of 
nutritional treatment on the susceptibility of certain varieties of chrysan- 
themum to rust. 
The young plants were then divided into four groups. A were fed as if for exhibition; 
B were grown normally; C were starved by being grown in small pots; and D were grown in 
a warm greenhouse. 
The rust developed on all the plants, but a luxuriant state of growth of 
the host favored the greater development of the fungous mycelium. 
Spinks (1913, p. 240) conducted an experiment on the susceptibility 
to rust of wheat plants grown in pots receiving different nutritive solutions. 
The data indicate somewhat higher susceptibility on the part of the plants 
richly fed with nitrogen. Stakman (1914, p. 16) finds that high fertiHzation 
of the soil increased the susceptibility to infection by Puccinia graminis 
tritici of resistant varieties of wheat, and so concludes that high fertilization 
is conducive to increased severity of rust attack on very resistant varieties 
as well as on susceptible forms. 
Indicating that the effect of specific nutrient substances is indirect, 
secondary to their effect on the vigor of the host, is the observation by 
Stakman and Levine (191 9, p. 72) that an application of sodium nitrate, 
excessive to the point of inhibiting the growth of the host, also inhibits the 
development of the rust and diminishes very perceptibly the size of the 
urediniospores. Ward (1902a) states that the size of the uredospores was 
not affected by starving the host. Stakman and Levine arrived at their 
observation that the size of the spores is affected by biometrical methods, 
which would cause to stand out distinctly size differences not apparent on 
gross examination. Ward does not give any spore measurements. 
Host Nutrition; Carbon Metabolism 
Intimate relation between the progress of a rust infection and the 
carbon metabolism of the host tissue has been demonstrated by Ward 
(1905), Fromme (1913), and Mains (1917). Sheldon (1903) studied the 
effect of light and temperature on rust development, and Stakman and his 
co-workers (191 7, 1919) have studied quantitatively the effects of Hght on 
the cereal rusts. 
Ward (1905, p. 40) refers to experiments on cereal rusts indicating that 
