DISEASES OP PLANTS. 155 



nnd by inoculation into healthy trees these are able to produce gumming. 

 There is at least one other type of bacteria not uncommon in tissues affected 

 by gummosis. From observations carried through one season it appears that 

 the disease spreads rapidly in the spring and very slowly or not at all during 

 the summer and autumn. At present it is said to be impossible to state posi- 

 tively that bacteria are responsible for all the more serious phases of the dis- 

 ease on the body of the tree or to indicate just what part they play in its 

 spread. 



For prevention and control the use of resistant stocks is advised, among 

 them being the Mazzard cherry and the Lambert cherry. Cutting out the 

 cankers and cutting off the small affected twigs have given evidence of being 

 valuable in controlling this disease, and the author urges growers to adopt this 

 practice. 



A partial bibliography is appended. 



Pear rust (Gymnosporangium sabinae), E. Scheibener (Gartenwelt, 17 

 (1913), No. 10, pp. 131-136, figs. 9).— The author states that G. sahince, the 

 cause of a rust in pear trees, employs as alternate host not only Juniperus sabina 

 but J. vii giniana, which is common as an ornamental tree, thus constituting 

 an additional menace to pear orchards. Parallel descriptions of these two 

 junipers are given, and the removal of both from the neighborhood of pear 

 culture is considered necessary. 



The black knot of plums, G. H. Coons {Mich. Farmer, 1J,0 (1913), No. 14, 

 pp. 425, 453, figs. 2). — A popular account is given of the black knot of plums, 

 which also affects cherries, with suggestions for its control. The fungicide 

 recommended is a dilute commercial lime-sulphur solution. 



The germination of the winter spores of grape downy mildew, L. Ravaz 

 and G. Verge (Prog. Agr. et Vit. (Ed. VEst-Centre), 34 (1913), No. 11, pp. 321- 

 331, figs. 8). — The authors conclude from a study of the germination of the 

 winter spores of Plasmopara viticola, which are to be found on fragments of 

 leaves, that it will be possible to foretell the probable time of the first attack of 

 the fungus on grapevines. 



Some investigations on the development and treatment of downy m.ildew, 

 H. Faes (Rev. Vit., 39 (1913), No. 999, pp. 161-165; Terre Vaud., 5 (1913), 

 No. 9, pp. 87-91, figs. 2). — The author reports negative results in attempting to 

 inoculate grape leaves with the winter spoi-es from old leaves, but a high degree 

 of success was attained when conidia were placed on the lower surfaces of the 

 leaves. Experiments in the germination of the oospores carried on at irregular 

 intervals from April 10 to July 8 failed to show any germination. The experi- 

 ments with infection by means of conidia are said to confirm observations pre- 

 viously reported (E. S. R., 26, p. 550) that infection is through stoma ta on the 

 lower sides of leaves. Spraying experiments in 1912 are considered to have been 

 unsatisfactory. 



Diseases of cacao and means for their control, L. Martinez (Bol. Dir. Gen. 

 Agr. [Mexico], Rev. Agr., 2 (1912), No. 6, pp. 520-.532). — The author discusses 

 a number of diseases of cacao with associated fungi, among which are a canker 

 of the shoots connected with Nectria thco'bromoe and Calonectria flavida; 

 brown rot of the pods, with Phytophthora fabcri or a Peronospora ; witches' 

 broom, with Exoascus theobromw or Colletotrichum luxificum; and a spreading 

 disease of the roots, with Macrophoma vestita and Lasiodiplodia theobroma'. 

 The latter of these is also associated with a black rot of the pods, and is said 

 to be a very important fungus in the Tropics. 



Remedies include removal and destruction of affected parts where practicable, 

 use of fungicides, and in general strict sanitation. 

 96700°— No. 2—13 5 



