338 GEORGE MASSEE [novembeb 



" 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. 



