338 GEORGE MASSEE [NOVEMBER 
“Plants of a variety of barley extremely liable to yellow-rust, which 
have been grown in sterilised soil in isolated glass houses, and have 
been protected against infection from outside, have sometimes become 
affected by yellow-rust.” 
“The yellow-rust appears in certain varieties of wheat and barley 
that are especially susceptible, uniformly four to five weeks after 
sowing.” 
“The results of these experiments prove beyond doubt that the 
disease must have come from an internal source, and have been in- 
herited from the present plant.” 
“The fungus lives for a long time a latent symbiotic life as a myco- 
plasma within the cells of the embryo of the cereal plant, and only 
enters upon a visible stage in the form of a mycelium a short time be- 
fore the pustules break out, and then only if the conditions are favour- 
able.” 
Eriksson was gradually led to adopt the idea expressed above 
after prolonged study upon the succession of rust on cereals, a detailed 
account of which is to be found in another book by the same author 
(6); also in considering that the various forms of spores or reproductive 
bodies would not account for the amount of rust produced. The con- 
clusions arrived at on this last point are summarised by the author as 
follows :— 
“The germinating power of the uredo and aecidiospores is often 
small, or at best capricious.” 
“The germinating power of the winter-spores (teleutospores) de- 
pends upon certain external conditions, and is restricted to a short 
period of time” (5). 
Now, if this theory proves to be true—that is, if it can be demon- 
strated that the protoplasm of a parasitic fungus can blend with the 
protoplasm of its host-plant, and remain passive in this condition from 
generation to generation until conditions are favourable for its manifest- 
ation in its own proper form as a parasite on the plant, in the proto- 
plasm of which it has for a certain period of time remained inert— 
many unsolved problems in Vegetable Pathology would be easily 
explained, or, at all events, the discovery would afford a very feasible 
explanation of phenomena at present inexplicable. If this theory had 
been evolved some few years ago, it would undoubtedly have explained 
in a satisfactory manner the occurrence of the common “smut” of oats 
(Ustilago avenae, Jensen). An old idea was that the oat plant was 
inoculated by “smut” spores when in bloom, the fungus afterwards 
developing in the ovary. This idea being disproved, the mycoplasma 
theory would have been useful; now, however, that Brefeld’s amply 
corroborated explanation of the life-history of “smut” has appeared, 
the necessity of mycoplasmic intervention has been superseded. The 
same will probably prove true in other instances. The weak point in 
the mycoplasma theory appears to be that it proves too much. 
