Observations and Experiments on Cereal Rusts. 153 
like a severe test; moreover after a frost or during a cold spell 
this rust too was very rare though not altogether absent. For 
these reasons it is doubtful, if one could safely attribute the 
outbreaks on the autumn-sown crop early in spring to the few 
uredospores that may be lurking in the open. This rust may be 
altogether absent during the greater part of a severe winter. 
Eriksson and Henning* have observed such a condition in 
Sweden. 
At the same time one cannot conclude, from the absence of 
uredo-sori even for the whole period during a severe winter, 
that uredospores from the last season’s crop have no significance 
as a source of infection to the autumn-sown (new) crops. The 
real source of danger is the abundance of uredospores on self- 
sown plants at autumn time and they will have done their 
work before the winter sets in. 
(b) Overwintering of the uredospores. 
As regards the viability of the uredospores of this rust taken 
from the open during winter, the writer agrees with Plowright f 
who found that spores which had been exposed to several nights 
of frost germinated with the greatest freedom. Further it may 
be added that during the last two seasons several inoculations 
on wheat were made in the open during winter with fresh 
uredospores of this rust resulting in satisfactory infections of 
the host. 
(c) Aecidium on Thalictrum. 
It is difficult to say anything definite on the possible infection 
of wheat by the aecidiospores found on species of Thalictrum. 
The aecidial stage on T. flavum in this country has been con- 
nected with P. persistens on Agropyron repens. It is interesting, 
however, to note that the brown rust of wheat was observed 
in plenty in the latter half of February (1921) and this year 
it was noted on the wheat crop in the middle of March, whereas 
the aecidium on 7. flavum occurs from May to July (Grove). 
Even if the aecidium on Thalictrum proves to be connected with 
P. triticina, it is unlikely to have anything to do with the fresh 
origin of that rust each year. 
* Eriksson, J. and Henning, E., Die Getreideroste (1896), 
t Plowright, C. B., Gard. Chron., N.S. Xvi, p. 234 (1882). 
t Grove, W. B., British Rust Fungi (1913). 
