1919] DISEASES OF PLANTS. 153 



stimuli, and that visible diffei'ence in response when brought about by para- 

 sites is due to the number and location of the parasites, age and kind of 

 tissues invaded, and volume, direction, and velocity of the stimulus exerted, 

 every case being primarily a physical stimulus due to changed osmotic pressure 

 rather than a direct chemical stimulus. He discusses briefly the factors 

 governing overgrowth in crown gall, some other types of plant galls, and crown 

 galls formed by extrusion of chemical substances and other effects of parasitic 

 excretions. References are given to literature on the subject. 



An automatic spore trap, F. D. Fkomme {Phytopathology, 8 (1918), No. 10, 

 pp. 5Jf2-544< fl'J- !)• — -^ description is given of a spore trap in which an alarm 

 clock revolves a Petri dish containing nonnutrient agar, the dish being covered 

 by a metal piece so arranged as to expose one-twelfth of the area of the dish 

 through an hour's time. This trap is said to have been used in studying the 

 dissemination of the basidiospores of Gymnosporangium juniperi-virginianw 

 with rather satisfactoi'y results. 



[Plant diseases and treatments], H. E., Watebbury (Bien. Rpt. Dept. Agr. 

 V.'ash., 3 (1017-18), pp. 84-87).— The results of tests with a third application 

 of iron sulphid or atomic sulphur for apple powdery mildew indicate that 

 such an application is justified, at least where the infection is pronounced, iron 

 sulphid being the cheaper and more effective. Some very good results were 

 secured by the use of lime-sulphur with atomic sulphur, the results being due 

 apparently to the more rapid volatilization, but these results were more 

 noticeable on the fruit than on the foliage and twigs. Milled sulphur is to be 

 tested in this connection. 



Potato seed tubers treated for Rhizoctonia for 1^ hours with corrosive 

 sublimate at a strength of i lb. to 30 gal. ot water showed results as good as 

 those obtained by treating for 2 hours or with a stronger solution. Apparently 

 the same treatment was effective against potato scab. 



Experiments with dust sprays applied under somewhat adverse conditions 

 yielded results not quite so good as those with lime-sulphur. 



Report of the division of plant pathology, C. W. Carpenter (Eaicaii Sfa. 

 Rpt. 1918, pp. 35-45, plf!. 3). — Among the diseases reported upon, the author 

 gives a further description of the banana freckle or black spot disease, 

 which has been previously noted (E. S. R., 38, p. 848). This disease seems to be 

 spreading rapidly, causing considerable loss, the infected plants producing 

 undersized, discolored and unevenly ripened fruit. The fungus attacks both 

 leaves and fruit, defoliating and weakening the plants and rendering the fruit 

 so unsightly that it is worthless for market purposes. The results of investiga- 

 tions of the fungus are given, and since the perfect stage is unknown the or- 

 ganism is tentatively described as Phoma niusce n. sp. For the control of this 

 disease, the author recommends sanitary measures. A fungus similar to P. 

 muscB has been found associated with a black spot disease of algaroba (Pro- 

 sopis chilensis) pods. 



Considerable attention has been given to diseases of the Irish potato, some 

 of which seem quite serious in Hawaii. The mite disease previously described 

 (E. S. R., 40, p. 644) is said to yield to dusting with dry sulphur or to spraying 

 with lime-sulphur spray. This trouble seems to be associated with dry weather, 

 and it is not anticipated that it will prove a serious menace to the potato in- 

 dustry at elevations of 1,.500 to 4,000 feet except in abnormally dry years. 

 Spraying experiments for the control of late blight are said to have given very 

 satisfactory results. A description is given of a potato variety which exhibits 

 considerable resistance to the late blight. 



Notes are given on coffee diseases, as well as miscellaneous insect and fun- 

 gus diseases observed during the year or not hitherto reported. 



