October 22, 1915] 



SCIENCE 



581 



cussed and certain peculiarities were described. 

 Possible connection with certain bacteria was 

 suggested and the nature and difficulties of 

 the problem concerned were discussed. In the 

 discussion which followed the paper Director 

 Ball, of Utah, and a number of others gave 

 their views on certain phases of the problem, 

 especially with regard to the relation of the 

 disease to insects. Mr. August Boncquet, of 

 Spreckels, California, gave support to the sug- 

 gestion that only insects which have been in 

 contact with diseased beets are capable of 

 transmitting the disease. 



Forest Pathology: E. P. Meinecke, U. S. D. A., 

 San Francisco. 



A number of forest diseases were exhibited, 

 including interesting and important rusts and 

 mistletoes. Several new hosts were shown in 

 the collection, and important but hitherto not 

 well-known forms were included in the demon- 

 stration. 



Northwestern Apple Anthracnose : H. S. Jack- 

 son, Corvallis, Oregon. 



Specimens were shown of the disease in 

 various forms, and the technical phases, par- 

 ticularly culture work and cross inoculations 

 with the different spore forms, were discussed 

 and the economic status of the disease briefly 

 indicated. 



The second session was held in the labora- 

 tory of plant pathology Thursday morning, 

 August 5, at 9 :30. 



Apple Mildew: W. S. Ballard, U. S. D. A., 

 Watsonville, Calif. 



The nature of this disease was explained 

 briefly, and an account of the history of the 

 efforts which have been made to discover effec- 

 tive control measures was given. Use of col- 

 loidal sulphur, prepared by dissolving sulphur 

 in melted resin, grinding and putting into am- 

 monia water, was described. The difficulties 

 involved in the use of sulphur in the California 

 coast districts on account of the danger of in- 

 jury to the trees were discussed and the rea- 

 sons for the use of unusually dilute spray 

 formulas were mentioned. 

 Mottled Leaf of Citrus Species: J. T. Bar- 

 rett, Riverside, Calif. 



Professor Barrett reviewed the main fea- 

 tures of this disease and showed typical speci- 

 mens. No specific cause has been discovered 

 and the disease is still classed as a non-para- 

 sitic disease. The diseased leaves contain more 

 starch than normally on account of defective 

 translocation, and apparently also an excess 

 of nitrogen. Some relation appears to have 

 been discovered between fertilization with ni- 

 trate of soda without the addition of vegetable 

 material and mottled leaf, but it was pointed 

 out that this is probably not a direct effect of 

 the materials used, but of the soil condition 

 produced, since in plots in which liberal use 

 had been made of the vegetable material the 

 disease has not appeared. The disease is be- 

 ing studied at Riverside from all possible 

 points of view and is being treated as a sta- 

 tion problem and not exclusively by any one 

 department. The possibility of an infectious 

 chlorosis is also being investigated. In the 

 discussion Professor P. S. Earle pointed out 

 that there are probably two distinct types of 

 mottled leaf in Cuba and the Isle of Pines, 

 arising from what is probably a specific dis- 

 ease of the small roots and from general un- 

 favorable soil conditions. 



Bacterial CanTcer of Cherry and Filbert Dis- 

 ease: H. P. Barss, Corvallis, Oregon. 

 Griffin showed the bacterial origin of the 

 bud blight in cherries. The identity of cause 

 for bud blight and body canker was shown by 

 the speaker by means of inoculations made in 

 the fall. Inoculations at other seasons were 

 not successful. The disease is most destruc- 

 tive during the first seven or eight years of 

 the life of the tree. It is now largely con- 

 trolled by planting Hazard apricot, prune and 

 Simone plum. 



The filbert disease is also caused by bacteria, 

 being in this case a yellow organism similar 

 to the walnut blight bacterium. A leaf spot- 

 ting and killing of twigs are produced and 

 cankers are formed, succulent tissue being sus- 

 ceptible. 



Crown Rot of Fruit Trees : Histological Stud- 

 ies: J. G. Grossenbacher, U. S. D. A., 

 Washington, D. C. (Read by title.) 



