Observations and Experiments on Cereal Rusts. ~ 151 
streaks on the stem. These streaks were fixed and microtomed 
but no mycelium could be discovered. No pustules of rust were 
noted on wheat even up to the 20th of May (nearly six weeks 
after inoculation). 
These negative results prove that sporidia cannot infect the 
graminaceous host directly. 
(f) Inoculations with aecidiospores. 
That the latter part of spring (1921) was unfavourable for an 
extensive infection of cereals by aecidiospores from barberry in 
this locality will be clear from the following observations. 
During the months of June and July as many as six attempts 
were made to inoculate seedlings of wheat and Couch grass 
with aecidiospores from barberry in the open, or with such 
material as had been cultivated in the laboratory. All the 
inoculations were made in a cool green-house. 
Excepting once, the aecidiospores from the open showed poor 
germination and out of thirty-six seedlings of Couch grass only 
three took infection. In the case of wheat (Red Sudan) out 
of forty-one seedlings only seven developed uredo-sori. The 
pustules on wheat it must be pointed out were exceedingly small 
(very much smaller than those on Couch grass). This form was 
later on found to be P. graminis secalis. 
In summing up one may state that as far as the neighbour- 
hood of Cambridge is concerned, and the same is probably true 
of other parts of England, the appearance of black rust year 
after year starts with the fresh infection of cereals by the 
aecidiospores from barberry. Also that there is no possibility 
of the perpetuation of this rust through overwintering uredo- 
spores, even after comparatively mild winters, like the two 
under report. 
The question of the possibility of the survival during winter 
by means of the mycelium inside the tissues of the host plant, 
will be discussed later on. 
4, THE Brown Rust (P. rriticina Erikss.). 
(a) Incidence. 
A study of the incidence of this rust, and its culture in the 
laboratory is interesting, as it combines the power of resistance 
to cold, so characteristic of yellow rust, with the capacity to 
withstand warmer weather, as exhibited by black rust. The rust 
is quite abundant in the neighbourhood of Cambridge and, as 
Grove* has mentioned, in England as a whole. It appears on 
* Grove, W. B., British Rust Fungi (1913). 
