i88 
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 ofif 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 (191 3, p. 238) describes an experiment on the susceptibiHty to 
Puccinia gliimarum 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 
KCl 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 
