Apr., 1922] 
RAINES — VEGETATIVE VIGOR OF THE HOST 
187 
is the strong suggestion, therefore, in Zavitz's data that the increase noted 
in the amount of rust present on oat plants grown at progressively greater 
distances apart is correlated with the increased luxuriance of growth of the 
host plants. 
Water -Culture and Sand-Culture Studies 
Ward (1902a) details two experiments on the susceptibility to rust in- 
fection of host plants which had been starved of essential nutrients. In 
the first experiment, 54 young seedlings of Bromus secalinus were used. 
The plants were grown in sand in 14 glass beakers, four to seven plants to 
a beaker, and watered with solutions of varying nutritive value. The 
plants in one beaker received only distilled water. The plants in another 
beaker received a cold-water extract of fresh horse dung, as a solution of 
high nutritive value. In a third beaker the plants received a full mineral 
nutritive solution (described as a ''normal nutritive mineral solution con- 
taining nitrates, phosphates, and sulphates of potassium, calcium, and 
magnesium"). The remaining eleven beakers received an incomplete 
nutrient solution, the elements omitted being respectively K; N; Mg; Ca; 
P; Fe; N and Fe; Mg and Fe; Ca and Fe; P and Fe. Inoculation was 
effected by applying uredospores of Puccinia dispersa to the leaves by means 
of a swab of cotton; at the time of inoculation the seedlings were 16 days 
old, counting from the time of sowing. 
Ward records detailed observations on the stature, robustness, color, 
and number of leaves of the seedlings in each beaker; on the time of appear- 
ance, number, and size of the pustules developed on them, and on the 
relative number of spores produced. Comparing the twelve seedlings 
which showed the most vigorous growth (6 which received the extract of 
horse dung, 3 the full nutrient solution, and 3 the full nutrient solution 
minus Fe, the plants averaging 20 cm. in height) with the ten poorest plants 
(4 receiving distilled water, 3 the full nutrient solution minus N, and 3 the 
nutrient solution minus N and Fe, the plants averaging 11 cm. in height), 
the observations recorded by Ward indicate that in the plants suffering 
from malnutrition (i) the incubation period of the rust was lengthened by 
one and two days; (2) the rust pustules were much smaller and produced 
fewer spores. In other words, a starved host meant a starved parasite. 
There is also the suggestion in the data that the starved seedlings showed 
a lower incidence of infection; but the small number of variables worked 
with, together with the large irregularity in dosage inherent in the method of 
inoculation used, compel reserve in making this deduction. 
A second experiment with 64 seedlings, duplicating the first, gave 
similar results. Regarding the spores produced on well nourished and on 
starved seedlings. Ward states that microscopic examination revealed no 
differences. Spores from starved seedlings could produce infection on 
other seedlings, similarly starved. 
