Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 
197 
older. On the other hand, Phleum pratense and Agrostis alba were more 
susceptible when older. 
Stakman and Levine (191 9, p. 73) observed an age difference in the 
progress of an infection of P. graminis avenae on oats. Plants that were 
one week old at the time of inoculation were somewhat more heavily in- 
fected at first than plants one, two, and four weeks older; but at the end of 
ten days the infection was heavier on the older plants, especially so on the 
plants that were three weeks old at the time of inoculation. The size of 
the urediniospores was uniform regardless of the age of the host, nor was 
any difference observed in the shape and color of the spores. They also 
state that 
. . . the junior author has obtained very successful infection on mature plants of more 
than a hundred different varieties of wheat, grown in the greenhouse and artificially inocu- 
lated with P. graminis tritici. 
Giddings (1918, p. 33) found susceptibility in apple leaves to infection by 
Gymnosporangium juniperi-virginiana to be limited to young leaves, not 
more than fifteen to twenty- four days old after unrolling from the bud, 
older leaves being almost completely resistant. H. H. York (personal 
communication) has found that the very young leaves of Ribes are resistant 
to infection by Cronartium ribicola, susceptibility not appearing until some 
time after the unfolding of the leaf. 
The factor of age and maturity of host tissue is reviewed here briefly 
because of its close association in thought with vegetative vigor. There is 
no necessary physiological connection between the two factors, and their 
significance in susceptibility and resistance to rust infection is probably of 
a different nature. The age factor in disease resistance is probably to be 
classed rather with varietal and constitutional differences than with physi- 
ological condition. 
Field Studies and Experiments 
A series of studies was made to determine the general facts as to the 
occurrence and epidemiology of the rusts on the cereal grains in the so called 
local-flora region of New York, and especially for the New York Botanical 
Garden and vicinity. Data as to the points involved were found to be 
very meager, and these preliminary studies were made as a contribution to 
the general problem of rust epidemiology in the Atlantic States, a field so 
far little studied because of the relative unimportance of grain growing in 
these regions. More especially also it was desired to lay a foundation for 
future studies of rust problems which presuppose a knowledge of the general 
behavior of the rusts under the climatic and other conditions of the region. 
The Rusts of the Cereal Grains and Related Grasses 
in the Vicinity of New York 
The time of first appearance, period of greatest virulence, and even the 
identity of the rusts on the cereal grains and related grasses which have been 
