VEGETATIVE VIGOR OF THE HOST AS A FACTOR INFLUENCING 
SUSCEPTIBILITY AND RESISTANCE TO CERTAIN 
RUST DISEASES OF THE HIGHER PLANTS 
II 
M. A. Raines 
(Received for publication July 13, 192 1) 
Further Field Studies and Experiments 
The Rust History of Plots of Cereals Sown at Successive Intervals 
through the Summer 
To test the susceptibility to rust of plants of different ages at each period 
of the summer and of young plants at difTerent times in the summer, and 
to follow the subsequent history of the disease on plantings of cereals 
started at successive intervals through the season, plots of wheat, rye, 
oats, and barley were started in the breeding plot of the New York Botanical 
Garden on June 10, June 23, July 6, July 20, August 5, and August 25, 1916. 
Observations were made at intervals on the height of the plants, the time of 
first appearance of the rust, the amount of infection, and the proportion 
of the rust in the teleuto stage. 
The results for the different cereals are shown in table 3 and are discussed 
below. In the table, the days on which the observations were made are 
given at the top. The height of the plants is given in inches When 
I the plants have headed, it is indicated by an ''H." The degree of rust 
infection is indicated by a numeral, and was estimated on a scale of 10, 
the values of the numbers in the scale being: i = an occasional pustule 
here and there; most of the leaves not affected. 2 = most of the leaves 
with from one to five sori. 3 = about ten pustules on each leaf. 4 = 
leaves heavily infected. 5 = leaves bearing the maximum possible amount 
of rust. 6 = leaf sheaths infected as well as the leaf blades. 7 = a 
sprinkling of rust sori on the stem and leaf sheaths; blades heavily infected. 
I 8 = infection on sheath and stem well developed. 9 = heavy infection 
on the stem. 10 = heaviest possible infection on the whole plant. The 
teleuto stage is indicated by its Roman numeral, "III." A fraction pre- 
I ceding the ''HI" gives the proportion of the rust in the teleuto form. 
As is indicated in table 3, the plots of wheat planted on June 10 and 
June 23 headed out in 77 and 64 days respectively. Those planted July 6, 
July 20, August 5, and August 25 never headed and never exceeded a 
height of 20 inches. The rust invariably appeared on the young plot as a 
thin, evenly distributed infection when the host plant was putting out its 
215 
