Observations and Experiments on Cereal Rusts. 163 
2. October 26th: 
Wheat inoculated in the open and kept —_ Pustules on the 
in the open 20th day. 
3. December oth: 
(2) Wheat inoculated in the open and ___ Pustules on the 
kept in the open 36th day. 
(b) Wheat inoculated in the laboratory — Pustules on the 
roth day. 
The question naturally arises, as to whether the black rust 
also can overwinter through its mycelium inside the host that 
may be infected in autumn. Observations on self-sown plants 
growing on the same plot unploughed, which had very badly 
diseased wheat till Oct-Nov. 1920 show that it is very unlikely, 
whereas the same plot was full of self-sown plants bearing yellow 
and brown rusts in plenty. The same might be said about this 
rust on Couch grass. 
The results of the following experiments on the incubation of 
black rust in the open suggest a similar conclusion. 
October 26th, rg2r: 
Seedlings of rye inoculated in the laboratory at the Botanic 
- Garden and removed to the open after two days—showed no 
- pustules (till Dec. rgth); the inoculated spots became dried 
and shrivelled. 
Control kept in intermediate pit. Pustules 12th day. 
It may be remarked, for the sake of comparison, that wheat 
inoculated with yellow and brown rust on the same date and 
kept side by side with the above showed pustules within 
twenty days. 
December roth, 1921: 
Rye inoculated in the laboratory at the Botanic Garden and 
removed to the open after three days; no pustules even after 
two months when most of the inoculated spots were dead. 
Control kept in intermediate pit showed excellent infection 
within three weeks. 
January 31st, 1922: 
(a2) Rye inoculated in intermediate pit and removed to the 
filmy fern house (very cool) after four, days; pustules 24th 
day. Temp. of pit 40-50° F.; casually up to 60° F. or above 
in bright sun. 
(6) Control. Pustules roth day. 
(c) Pot removed to the open. Pustules on the 30th day; 
only three out of twenty spots inoculated, developed pustules. 
February 4th, 1922: 
(2) Wheat inoculated and kept in unheated greenhouse. 
Pustules 25th day. 
es 
