1 88 AMERICAN JOURNAL OF BOTANY [Vol. 9, 



In 1905, Ward reports experiments indicating that starving the host 

 tissue after infection has taken place has an adverse effect on the growth 

 of the fungous mycelium. He cut off infected leaves of cereals on the third 

 day after artificial inoculation and floated them on water. Histological 

 examinations of the leaves indicated that the rust fungus in the tissues 

 continued to grow for a time, but soon showed signs of starvation. 



Spinks (1913, p. 238) describes an experiment on the susceptibility to 

 Puccinia glumarum of wheat plants grown in water cultures. He used six 

 plants grown in each of three solutions: a standard nutrient solution (Det- 

 mer's) ; a nutrient solution containing four times the quantity of ammonium 

 phosphate; and a nutrient solution containing four times the quantity of 

 potassium chloride. The cultures were inoculated by applying uredospores 

 to the leaves; they were then set outdoors, so that further spread of the 

 rust occurred naturally. Spinks gives no data on the condition of the 

 plants, and this can only be inferred from the mode of treatment they re- 

 ceived. The data presented indicate that the plants growing in the nutrient 

 solutions containing a four-fold concentration of nitrogen were more sus- 

 ceptible than those in the standard solution. Excess concentration of 

 KC1 gave an apparent slight depression of susceptibility. 



Stakman (1914, p. 39) reports some experiments with Puccinia graminis 

 tritici on wheat seedlings grown in water cultures. In an experiment in 

 which nitrogen and phosphorus were omitted from the culture solutions, 

 the check plants were more severely attacked than the experimental plants. 

 Summarizing his results, Stakman says (p. 48) : 



It was found that in general the absence or presence in excessive amounts of various 

 nutrient substances, such as nitrogen and phosphorus salts, did not directly affect the 

 immunity or susceptibility of wheats. Conditions favoring a normal development of the 

 host were conducive to a vigorous development of the rust. The action of fertilizers, either 

 natural or artificial, is probably indirect. 



Soil-Culture Experiments 



Sheldon (1905, p. 226) remarks on the low susceptibility shown by 

 poorly growing carnations to artificial infection with Puccinia Caryophylli: 



The results show that the plants that were making a vigorous growth were more sus- 

 ceptible to artificial infection than those that were making little or no apparent growth. 

 A few slowly growing plants were repeatedly inoculated without success until the plants 

 were given extra care and stimulated so that they began to grow more vigorously. Some 

 carnations, grown in small pots, were each inoculated five or six times at intervals of about 

 twenty days without any of the inoculations being effective. These plants grew very 

 slowly, were slender, and produced only one, or at most two, small blossoms. 



In the same paper (p. 228) Sheldon reports an experiment on the length 

 of the incubation period of the carnation rust in which he inoculated simulta- 

 neously 170 pinks growing in soils of varying nutritive values. The plants 

 had been derived by taking sets of cuttings from the same stock plant, a 



