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 increasec} 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 ol 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 fertilization 

 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 (1919, 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 (i9O2a) 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 (1917, 1919) have studied quantitatively the effects of light on 

 the cereal rusts. 



Ward (1905, p. 40) refers to experiments on cereal rusts indicating that 



