1917] EXPERIMENT STATION RECOED. 549 



DISEASES OF PLANTS. 



A method for studying the humidity relations of fungi in culture, N. E. 

 Stevens {Phytopntlwlogy, 6 (1916), No. 6, pp. 428-432). — A description is given 

 of a method used by the author in maintaining known humidities in small 

 chambers which is applicable to the study of fungi in culture or growing on 

 small fruits. It consists in keeping the cultures of fungi or the affected fruits 

 in an atmosphere which is maintained at a constant humidity by exposure to an 

 aqueous solution of sulphuric acid of known specific gravity. 



Celluloid cylinders for inoculation chambers, E. E. Hubert (Phytopathology, 

 6 (1916), No. 6, pp. 447-450, fig. 1). — The author describes a cylinder made of 

 sheet celluloid which has proved adapted to use in inoculation experiments on 

 tree seedlings and similar hosts. 



Nematode technique, T. B. Magath (Trans. Amer. Micros. Sac, S5 (1916), 

 No. 4, pp. 245-256, figs. 6). — The methods here presented are intended to serve 

 as a guide for future work. While applicable for free-living nematodes, the 

 methods have been worked out particularly for the parasitic forms. 



Presence of nitrites and ammonia in diseased plants. Its significance 

 with regard to crop rotation and soil depletion, P. A. Boncquet (Jour. Amer. 

 Chem. Soc, 38 (1916), No. 11, pp. 2572-2576).— The author, having continued 

 some phases of the work previously participated in by him (E. S. R., 34, p. 

 645), states that in beets Bacillus morulans is able to reduce nitrates not only 

 to nitrites but also partly or wholly to ammonia, these substances never being 

 found in these tests apart from pathological indications. 



Mosaic disease of tobacco was associated with a filterable organism which 

 showed considerable reducing power and which was absent from normal leaves. 

 An organism provisionally named Streptococcus solani n. sp. was present uni- 

 formly in certain potato vines and leaves. This proved to be an active nitrate 

 reducer. Traces of ammonia were also detected. This organism may prove 

 to be connected with brown streak and blossom abortion of potato. Some 

 other plants which looked sickly gave a decided nitrite reaction, the intensity 

 thereof corresponding to the severity of the sickly appearance shown by the 

 plants. 



Nitrites have not been detected in any plant tissue which can, in strictness, 

 be called normal. The disturbance is ascribed to a partial and local nitrogen 

 starvation of the tissues, as well as to mechanical laceration due to ulcer forma- 

 tion by the bacteria. 



It is thought that soil depletion has a fundamental relation to nitrate re- 

 duction, a lack of rotation favoring the accumulation of nitrate-reducing 

 organisms. 



The influence of .fficidium clematidis on the leaves of its host, L. Monte- 

 MABTiNi (Riv. Patol. Veg., 8 (1916), No. 8-9, pp. i65-i76).— Having shown pre- 

 viously (E. S. R., 17, p. 981) that vegetable parasites produce in their hosts 

 at first a stimulating, but later a depressing effect, the author has made a 

 study of leaves of Clematis vitalba attacked by ^. clematidis, from which it 

 is concluded that the acceleration observed is a consequence of the increase 

 of chlorophyll in the infested leaves. While the ash weight per unit of area 

 was increased by the fungus attack, the ash weight per unit of dry matter was 

 lessened thereby. Assimilation and transpiration appeared to be more ener- 

 getic in diseased leaves than in sound ones, as shown by the total ash content. 

 The calcium, however, was somewhat less in case of the diseased leaves, which 

 showed a considerable increase in silica. These findings are compared with 

 some reported by Pavarino (E. S. R., 18, p. 347). 



