Observations and Experiments on Cereal Rusts. 145 
Klebahn* has remarked that in Germany P. dispersa and 
P. glumarum can overwinter in the uredo-stage, but P. graminis 
cannot do so. 
On the other hand Eriksson and Henning} state that in 
Sweden none of the three rusts under report can overwinter in 
the uredo-stage. 
In India Butler { has stated that self-sown plants are very rare 
and probably quite absent in the hotter parts of that country, 
where, like Australia, the period most critical for rusts is the 
intensely hot summer. He has further remarked that attempts 
to preserve uredospores in the earlier part of the hot weather 
have been unsuccessful. 
From a cursory perusal of the observations quoted above it is 
clear that on account of great climatic differences between the 
countries referred to, the incidence of rusts could not possibly 
have been similar. Apart from its incidence one has to enquire 
whether a certain rust can or cannot pass the unfavourable period 
inside the host in the mycelial stage. Again it is doubtful if the 
small number of uredospores that may have survived through 
the critical period would be enough to bring about a “spon- 
taneous outbreak”’ of a certain rust. This question becomes still 
more difficult to answer in view of the fact, which will be proved 
later, that in a cold country rusts take a much longer time to de- 
velop pustules even during spring than has hitherto been believed. 
2. Eriksson §, as is well known, has attributed the fresh out- 
break of rusts to an internal, inherited and invisible germ of 
disease inside the seed grain which he considers may take from 
two weeks to nine months from the time of sowing to assume 
a visible form, but there are few believers in this “mycoplasm 
hypothesis” at the present day. 
Bolley || has stated in contradiction to Eriksson’s view that 
there is much evidence that all infection of new grain plants 
comes from without, and that there is nothing to prove an 
internal symbiotic life. Similarly the negative results obtained by 
Marshall Ward in his pure culture experiments with seeds from 
rusted grasses, and those conducted by Butler and Hayman** 
at Cawnpore, prove conclusively that no rust develops from the 
“mycoplasm’”’ suspected of being inside the seed grain. 
* Klebahn, H., Die Wirtswechselnden Rostpilze (1904). 
t Eriksson, J. and Henning, E., Die Getreideroste (1896). 
{ Butler, E. J., Fungi and Disease in Plants (1918). 
§ Eriksson, J., Compt. Rend. cxxiv, p. 475 (1897); Ann. Bot. xIx, p. 55 
Be Bottey, H. L., Proc. Amer. Assoc. Adv. Science, xtvu1, p. 408 (1898). 
{| Ward, H. M., Ann. Bot. x1x, p. 1 (1905); Proc. Roy. Soc. LxIx, p. 451 
Bee Batter E. J. and Hayman, J. M., Mem, Dept. Agric. India, Bot. Ser. 1, 
No. 2 (1906). 
M.S. ze) 
