250 EXPERIMENT STATION RECORD. fVol. 40 



the present paper do not support the conclusions of previous workers that the 

 pathogenicity of biologic forms is easily changed by host influence. From the 

 practical standpoint the constancy of biologic forms is considered of great im- 

 portance, and it is believed that breeding for rust resistance can proceed with 

 considerable assurance that the same rust will not adapt itself quickly to new 

 varieties. Biologic forms are believed to have arisen either by mutation or by 

 gradual process of evolution. These processes may be still operative, but the 

 authors have been unable to detect any mutation or to produce any perceptible 

 evolutionary changes experimentally. Tbe possible role of hybridization is to 

 be investigated. 



Angular leaf spot of cucumber: Dissemination, overwintering, and control, 

 E. Caksner (Jour. Agr. Research [U. 8.1, IS (1918), No. 3. pp. 201-220. pU. J,, 

 figs. S). — A report is given of cooperative investigations, carried on by the 

 Wisconsin Experiment Station and the U. S. Department of Agriculture, on 

 the dissemination, overwintering, control, and other data regarding the angular 

 leaf spot of cucumber. This disease, which is said to be due to Bnrtcrium 

 lachrymans, is believed to be world-wide in its distribution and is regarded as 

 of considerable economic importance. 



Infection occurs in both leaves and fruit, thp organisms entering the plant 

 through the stoniata. Evidence has been obtained indicating that the causal 

 bacteria overwinter in the seed, and seed treatment is believed to offer the 

 greatest hope of satisfactory control. The causal organism is sensitive to 

 desiccation, is readily killed in artificial media by freezing, and is also readily 

 killed by dilute solutions of formaldehyde, copper sulphate, or mercuric chlorid. 

 No marked difference in varietal resistance or susceptibility has been found 

 among horticultural varieties of cucumbers. Infection by this organism seems 

 to be limited to cucurbits, a few ornamental gourds beintr attacked by the 

 disease, but the cucumber appearing to be the only one seriously affected. 



Sanitary measures, such as precautions in picking and in insect control, may 

 be helpful, and spraying with Bordeaux mixture checks the disease, but is not 

 thought by the authors to be practicable on a commercial scale. 



Anthracnose of cucurbits. M. W. GabDNEB (17. 8. !><pt. Agr. lUil. 727 (1918). 

 pp. 68, pis. 8, flg». 15).— The results are given of studies carried on under co- 

 operative arrangement between the Bureau of Plant Industry. T T . S. Depart- 

 ment of Agriculture, the Wisconsin Experiment Station, and certain cucumber 

 growers during the seasons of 1915. 1910. and 1917. 



The fungus CnUctotrichum lagenarium, the cause of anthracnosp of cucurbits, 

 is said to be limited to hosts of the family Cucurbitaceje. being of greatest 

 economic importance on cucumber, mnskmelon, and watermelon. In addition 

 other species of cucurbits are reported to be subject to attack, but anthracnose 

 has not been found as a vine disease on species of the genus Cueurbita, which 

 includes squash, pumpkin, and certain gourds. Serious losses are reported to be 

 caused to the watermelon-growing industry and among cucumbers grown for 

 slicing purposes, the loss in the pickle crop not being very great. Leaves, stems, 

 and fruits are attacked, and the plants may be killed or the fruit blemished 

 so as to be practically worthless. 



Studies are reported on the life history of the causal organism in relation 

 to the disease. It is claimed that it spreads in the field from centers of one 

 or two infected plants, the spread being rapid following rainy periods when the 

 temperatures are not far from 75° F. The principal agencies of dissemination 

 in the field are rain and surface drainage wafer. The disease has been noted 

 as especially destructive in fields where artificial overhead watering is prac- 

 ticed, and evidence has been obtained that it has been spread by the hands 



