DISEASES OF PLANTS. 55 



Grape mildew, L. Ravaz (Min. Agr. [France], Ann. Serv. Epiphyties, 1 

 {1912), pp. 302-398, figs. 2). — This coutribution deals with, the relations between 

 soil surface conditions and the development of Plasmopara viticola, reporting 

 also some experiments with fungicides. 



Some experiments in treating- citrus trees for gummosis and heart rot, 

 J. A. Pkizer {Mo. Bui. Com. Hort. Cat., 4 {1915), No. 1, pp. 7-19, figs. 7).— A 

 description is given of the brown rot gum disease of the lemon, due to Pythi- 

 acystis citrophthora, and the gi'ay fungus gummosis, caused by Botrytis vul- 

 garis. 



In addition an account is given of successful experiments for the control of 

 these diseases, which consisted in cutting out the diseased bark and painting 

 the area over with Bordeaux i>aste. This has been practiced for some time 

 for the treatment of the brown rot at an annual cost of about 7 cts. per tree 

 in a block of over 18,000 trees. Similar results have been obtained for the 

 control of the Botrytis disease. 



Report of plant physiologist, B. F. Floyd {Florida St a. Rpt. 1914, pp. 

 XXX-XXXV, fig. 1). — In a study of the relation of the water table to die-back 

 of citrus trees, conditions were produced that were believed to be similar to 

 those in groves lacking drainage. Tanks were arranged in series, in the first 

 series of which the water table stood 7 in. from the soil surface, in the second 

 14 in., and in the third the soil was kept moist to the bottom of the tank without 

 allowing saturation. Orange trees of uniform size, appearance, and thrift were 

 planted in these tanks in 1912, and the resulting growth has been measured and 

 analyzed. 



It was found that the types of growth produced were not at all the same that 

 characterize trees which develop physiological disturbances known as die-back. 

 It is concluded, therefore, that the experiment did not exactly reproduce the 

 field conditions known as lack of drainage, which is held to cause this disease. 



Report of plant pathologist, H. E. Stevens {Florida Sta. Rpt. 1914, pp. 

 LVII-LXXIV). — Field studies, infection experiments, and experiments for the 

 control of gummosis are reported upon, most attention being given to the form 

 of gumming which is commonly known as gummosis, a brief description of 

 which has been given (E. S. R., 19, p. 654). Two types of this disease are rec- 

 ognized, one of which attacks the trunks, larger branches, and smaller tvngs, 

 while the other occurs only on the trunks and larger branches. 



The cause of gummosis has not been definitely established, although several 

 fungi are found associated with it. Observations have been made on the devel- 

 opment of diseased areas, which indicate that the development of the disease is 

 slow and that there are active and passive phases associated with this develop- 

 ment. Inoculation experiments were made with diseased tissue inserted in 

 healthy trees, but no definite conclusions are drawn from the results. It is 

 thought that probably young trees are more resistant to the disease than older 

 bearing ones. Some control experiments are briefly reported, in which the dis- 

 eased portions of the tissues were cut out and treated with antiseptics. For 

 this purpose Bordeaux paste was found fairly effective. 



The investigations with melanose were continued, and the inoculation experi- 

 ments showed that Phomopsis citri is the cause of both the stem-end rot and 

 melanose (E. S. R., 31, p. 750). It is stated that severe outbreaks of stem-end 

 rot occurred in different localities during the season, and this is believed to be 

 due to the unusual development of the fungus In dead citrus twigs. 



A brief report is given "on the citrus canker, a preliminary but more detailed 

 account of which has been issued by the station (E. S. R., 31, p. 54). It is 



96619°— Xo. 1—15 5 



