34° GEORGE MASSEE [novjsmber 



black rust — Puccinia graminis. No trace of yellow rust — Puccinia 

 glumarum — was present. 



The following season the remaining half-pound of wheat was sown 

 under conditions precisely similar to those described above. The 

 plants protected by glass globes remained perfectly free from rust of 

 any kind, whereas the seed sown on manure, and fully exposed to 

 atmospheric conditions, showed at the expiration of thirteen weeks, 

 twenty-eight per cent of rusted plants ; the rust being Puccinia 

 graminis. Not a trace of yellow rust — Puccinia glumarum — was 

 present. 



Kemembering the clause in Eriksson's theory that the mycoplasma 

 only assumes a visible form " if the conditions are favourable," I am 

 ready to admit that both my out-door and other experiments with 

 " Horsford Pearl " were not grown under the conditions necessary for 

 the conversion of mycoplasma into mycelium, nevertheless my experi- 

 ments are not unique in this respect. 



McAlpine of Melbourne records having received from Eriksson ten 

 varieties of wheat showing in a marked degree powers of resistance to 

 yellow rust — Puccinia glumarum. When sown in Australia all the 

 varieties were attacked by one or other of the native rusts — Puccinia 

 dispersa, or P. graminis. No trace of yellow rust — P. glumarum — was 

 observed (8). 



These experiments corroborate at least what has previously been 

 stated (9), that cereals especially susceptible to one form of rust in a 

 particular country, may, if sown in another country, lose their suscep- 

 tibility for the original kind of rust, and prove equally susceptible to 

 another form. 



As to whether this also proves that mycoplasma does not in reality 

 exist, or that a change of locality destroys a mycoplasma that 

 previously existed, I am not at present prepared to say. 



Another set of experiments with wheat, commenced before the 

 mycoplasma theory was published, were conducted for the purpose of 

 endeavouring to ascertain whether mycelium passed into the seed in 

 those cases where the mycelium of a parasitic fungus was undoubtedly 

 present in the fruit. 



This line of research was suggested by a remark made by Collenette 

 (10), who in writing on the Tomato disease in Guernsey, says: — "My 

 theory, then, is that the ' sleeping ' disease is really primarily pro- 

 pagated by the seed, and the first thing to be done is to refuse to save 

 or use the seed derived from the diseased plants." Collenette's theory 

 was founded on the discovery of delicate hyphae in the tissue of tomato 

 seed produced by a diseased tomato. I also had an opportunity of 

 examining some seed obtained from a diseased tomato, kindly furnished 

 by Mr. Collenette, and succeeded in detecting slender, hyaline hyphae 

 about 2/u, thick in the testa of the seed, but at the time was not able 

 to demonstrate that these hyphae were genetically connected with 



