DISEASES OF PLANTS. 447 



Citrus canker, III, H. E. Stevens (Florida Sta. Bui. 128 {1915), pp. 20, figs. 

 6). — In continuation of observations on citrus canker (E. S. R., 32, p. 345), the 

 author gives an account of the history of the disease, its distribution in Florida, 

 a description of its effect on the host plant, the cause of the disease, and 

 laboratory investigations on the organism, Pscudomonas ciirl, in which its 

 growth in sterilized soil and the effects of high temperature and drying out were 

 noted. 



In the laboratory experiments, soil was sterilized, inoculated with cultures of 

 the bacteria, and kept under observation for six months, at the end of which 

 period the bacteria were found alive and active. The organism was found to 

 sustain high temperatures and drying out, which is believed to be an additional 

 factor in spreading the disease. 



Prompt and complete destruction of all infected trees is considered the only 

 practical method of control, and since the bacteria are capable of living and 

 growing in unsterilized soil for a long period, it is thought dangerous to plant 

 citrus trees on laud where the canker has been found. 



A powdery mildew on citrus, C. N. Carter (Phytopathology, 5 (1915), No. S, 

 pp. 193-19G, pi. 1, fig. 1). — The occurrence of a powdery mildew on the Dancy 

 tangerine in southern California is reported. The fungus so far has been found 

 only in a limited area, and is restricted to this tangerine. 



The author believes this to be the first report of this type on citrus plants. 

 The name Oidiitm tingitanium n. sp. is proposed for this mildew, a technical de- 

 scription of which is given. 



A bacterial disease of the mango, Bacillus mangiferse n. sp., Ethel M. 

 DoiDGE (Ann. Appl. Biol., 2 (1915), No. 1, pp. 1-45, i)ls. 14, figs. 3; abs. in Agr. 

 News IBarbados], 14 (1915), No. 349, p. 302). — A disfiguring and rotting disease 

 of mangoes is described as having caused much loss and alarm in South Africa 

 in recent years. The causal organism, which is described as B. inangifcrw 

 n. sp., is carried partly by water dripping from affected portions of the plant, 

 but a more important carrier is found in air movements. Lignified tissues are 

 not aifected, but the organism invades parenchymatous tissues, wedging apart 

 and killing the cells and causing dark, angular spots on the leaves. Other soft 

 portions of the plant are also attacked. The symptoms are described as very 

 characteristic. 



The organism was not controlled by use of Bordeaux mixture, iron sulphid, 

 or Hycol. The organism is described in detail, and a resume is given of its 

 salient characters. 



Melaxuma of the walnut (Jug'lans reg-ia), H. S. Fawcett (California Sta. 

 Bid. 261 (1915), pp. 131-148, figs. 5). — A preliminary report is given of a disease 

 of English walnuts in California, which has been under observation since 1913, 

 and brief accounts of which have been previously noted (E. S. R., 84, p. 5G). 



This disease, which is given its name on account of the black sap excreted, 

 causes black cankers on the trunk, crotches, and large limbs, and occasionally 

 the wilting of small branches. Experiments have shown that the cankers, as 

 well as the wilting of the branches, are caused by the fungus Dothiorclla gre- 

 garia, which has been isolated, grown in pure cultures, and found to produce 

 the typical symptoms of the disease. In addition to the walnut, the fungus has 

 been found on a species of willow (Salix lasiolcpis) , from which it is thought 

 to have spread to walnut trees. 



Experiments have shown that the disease may be successfully controlled by 

 cutting out the cankers and the dead and badly diseased limbs, and disinfect- 

 ing the cuts. On account of the willow acting as a host of the fungus, it is 

 recommended that all willows near walnut orchards be cut back. 



