Pflanzenkrankheiten. 149 



advisability of carefully collecting and burning all plant refuse after 

 harvest, especially when the field was badly diseased. 



M. J. Sirks (Haarlem). 



Fawcett, H. S., The known distribution of Pythiacystis cy- 

 trophtJioni and its probable relation to mal digomma of 

 Citrus. (Phytopathology. V. p. 66—67. 1915.) 



The lemon brown rot fungus, Pythiacystis citrophthora (Sm. and 

 Sm.) seems to be very wide-spreaded about the world; previously 

 (1913) it was reported by the author to be the causal agent in one 

 form of lemon gummosis in California; since the author found 

 the fungus also in Florida, Cuba and Isle of Pin es, and R. E. 

 Smith in Sicily and perhaps in Valencia, Spain. Not only 

 lemonbark and lemonfruits are affected by the fungus; inoculation 

 experiments so far carried out in California, together with the 

 finding of the fungus in Mal di gomma specimens of oranges in 

 Florida, indicate that in addition to being the cause of lemon 

 brown rot and one form of lemon gummosis, P. citrophthora may 

 also be at least one of the causal agents in the occurrence of Mal 

 di gomma. The orange bark, being somewhat more resistant than 

 lemon bark, reacts differently to the attack of this fungus, This fact 

 appears to explain the difference in the general appearance of Mal 

 di gomma in oranges and of lemon gummosis in California. 



M. J. Sirks (Haarlem). 



Harter, L. L., Notes on the distribution and prevalence 

 of three important sweet potato diseases. (Phytopatho- 

 logy. V. p. 124-126. 1915.) 



The paper contains the results of investigations about the distri- 

 bution in America of the following three important Batatas- 

 diseases: Stem rot (caused by Fusarium hyperoxysporum Wr. and 

 F. batatatis Wr.), Blackrot (caused b}^ Sphaeronema fimhriatiim 

 (Ellis and Hals.) Sacc.) and Foot rot, a comparatively new disease 

 (caused by Plenodomus destruens Harter). 



M. J. Sirks (Haarlem). 



Hartley, C. and T. C. Merrill. Storm and drouth injury 

 to foliage of ornamental trees. (Phytopathology. V. p. 20 — 

 29. 1915.) 



The unusually hot and dry season of 1913 with a number of 

 severe local storms gave the authors occasions for studying dama- 

 ges caused by drought and by storm, especially on Norway maples, 

 sugar maples, sycamore maples, pine oak, man)'- species of conifers 

 a. o. Cases of drougth and storm injury are described in this paper 

 and partly figured. 



Interesting are these concluding remarks: „So far as could be 

 observed the drouth preceding the storm was not a predisposing 

 factor to storm injury, as trees which had previously shown drouth 

 injury were not more damaged by the storm than trees which had not 

 shown drouth injury, and street trees were less affected than those 

 in open parks. It is presumed that most of the damage was caused 

 by the breaking of cell walls in the leaf inferior with consequent 

 loss of water holding capacity." The descriptions and other remarks 

 must be read in the paper itself. M. J. Sirks (Haarlem). 



