338 SUMMARY OF CURRENT RESEARCHES RELATING TO 



host-plant is starved, the germ-tube is unable to establish itself. What- 

 ever affects the host affects the parasite also. When plants were deprived 

 of some constituent necessary to healthy growth, infection spots showed 

 corrosion and collapse instead of normal rust-flecks. The paper is 

 enriched by tabulated results of experiments and by figures of the tubes 

 used in growing the grasses. 



Rust of Cereals.* — Jakob Eriksson has completed the publication of 

 his studies on rusts. In the first part of the work he gave an account 

 of the disease itself and the results of his many culture experiments,, 

 carried on during several years, with the purpose of determining 

 the source of infection. All attempts have failed, he considers, to 

 explain the origin of rust by infection from fungus spores that have 

 survived the winter ; nor can it be traced to spores or mycelium in the 

 grain. He finds in the tissue of the host-plants, in the cells bordering 

 on the rust-pustules, special corpuscles, irregular in form, somewhat 

 bent, and simple or branched. These have arisen, he says, from a 

 mycoplasma in the cell, and they produce the mycelium of the fungus. 

 He considers the presence of the mycoplasma in the plants, from the 

 seed onwards, as a case of symbiosis which may not always be hurtiul 

 to the development of the host. 



]n a third part he discusses the papers that have been published 

 since first he announced his mycoplasma theory in 1897. The final 

 part of his paper deals with the best methods of combating the disease. 

 He strongly recommends experimental stations in the countries that are 

 affected by the rust-disease, that the different factors concerned in the 

 propagation of tbe fungus may be discovered, and that information on 

 such points as soils, manures, &c. may be imparted to the growers ; also 

 that experiments should be carried out to test which varieties of grain 

 are likely to be less affected by disease than others. 



Diplodia cacaoicola.f — This fungus, parasitic on sugar-cane and 

 cacao in the West Indies, has been thoroughly worked out by A. Howard. 

 It is a rind-fungus and forms colonies of pycnidia containing two-celled, 

 brown spores just under the bark, which it finally ruptures. The author 

 was able to grow the fungus saprophytically from spore to pycnidium, 

 and to reinfect young plants with material produced in his cultures in 

 the laboratory. By comparison and experiment he proved the morpho- 

 logical identity of the fungi causing the rind-disease on sugar-cane and 

 cacao ; and by infection experiments from one host-plant to the other, 

 he was able to establish that they were identical biologically. He 

 advises planters as to the best method of combating the disease. 



Canker of the Oak. J — M. C. Potter has found many cankered oaks- 

 in the north of England and has traced the injury to the presence of a 

 fungus belonging to the genus Stereum. Pure cultures were made of 

 the suspected fungus, and these were used to infect successfully oak 

 branches. Miniature cankers were produced, resembling those found 

 on the diseased oaks. The author discusses the different species of 



* Ann. Sci. Nat., ser. 8, xv. pp. 1-155 (5 pis.). 



t Ann. JBot, xv. (1901) pp. 683-701 (1 pi.). 



t Trans. Eng. Arb. Soc, 1901-1902, reprints, 8 pp. and 4 figs. 



