Apr., 1922] RAINES VEGETATIVE VIGOR OF THE HOST 197 



older. On the other hand, Phletim pratense and Agrostis alba were more 

 susceptible when older. 



Stakman and Levine (1919, 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 

 Gymno sporangium juniperi-mrginiana 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 



