144 Transactions British Mycological Society. 
carried on for a period of nearly two years, with the object of 
throwing further light on some of the more important physio- 
logical differences between the yellow, the brown, and the black 
rusts of wheat. 
2. REVIEW OF THE LITERATURE. 
It is unnecessary to enter into a historical survey of the work 
done on the cereal rust problem, in view of the fact that it has 
so often been summarised. In referring to comparatively recent 
work in different countries, my object is to-bring out the 
various views expressed on the significance of the more im- 
portant factors that fall within the scope of this paper. 
1. Dealing first with the possibility of the uredospores oc- 
curring during the critical periods on self-sown plants being 
the source of infection, one may refer to the observations made 
by McAlpine* in Australia. In that country Puccinia graminis 
is perpetuated from season to season by means of uredospores. 
It is important in this connection to note that in Australia it 
is the heat and drought of summer, and not the winter cold, 
against which the fungus has to provide. 
In some parts of the United States of America, Carleton}, 
Hitchcock and Carleton{ and Bolley§ have remarked that fresh 
uredospores of Puccinia Rubigovera are found throughout winter. 
In a later contribution Bolley|| has stated that the uredospores 
of P. graminis also can withstand the cold of a North Dakota 
winter. Carletont, however has denied the possibility of the black 
rust (P. graminis) of wheat being able to overwinter in Kansas. 
Again Pritchard§] has pointed out that the uredospores of 
P. graminis when kept in the open lost their viability in two 
months’ time. The same author also remarked that in North 
Dakota the wintering of P. graminis as mycelium in plant 
tissues is very doubtful. 
Hoerner** has made a similar observation about the brown 
rust of oats. 
Jaczewskiff has stated that black rust in Russia cannot over- 
winter and that even the mycelium of this rust inside the host 
cannot withstand frost. 
* McAlpine, D., The Rusts of Australia (1906). 
ft Carleton, M. A., U.S. Dept. Agric. Div. Veg. Phys. and Path. Bull. No. 16 
(1899). 
t Hitchcock, A. S. and Carleton, M. A., Kansas Agric. Coll. Exp. Stat., 
Bull. 46 (1894). 
§ Bolley, H. L., Centralbl. f. Bakt. Iv, Abt. 2, p. 893 (1898). 
|| Bolley, H. L., Science, xxiI, p. 50 (1905). 
4| Pritchard, F. J., Bot. Gaz. Li1, p. 169 (1911). 
** Hoerner, G. R., Amer. Journ. Bot. vit, p. 452 (1921). 
tt Jaczewski, A., Zeitschrift fiir Pflanzenkrankheiten, xx, p. 321 (1910). 
