ANNUAL REPORT, 1937 37 



may be identified only by laboratory diagnosis. Since the establishment of the 

 Shade Tree Laboratory in June 1935, approximately 5700 specimens have been 

 received for diagnosis. During 1937, laboratory studies of more than 700 speci- 

 mens, including collections by 4 field men, were completed by cultural and mi- 

 croscopical methods. Sixty-six diseases of 32 hosts, including 12 diseases of elm, 

 were studied during the year. 



Experiments, initiated in 1936, on potted elms of several species inoculated with 

 fungus parasites of elm known to be present in Massachusetts have been con- 

 tinued in the greenhouse during the past year. 



A detailed study^ of the State-wide distribution of elm wilts associated with 

 Cephalosporium and Verticillium was completed by Miss Eunice M. Johnson, 

 Institutional Fellow in Botany. 



Cytospora Disease of Spruce. (C. J. Gilgut, Waltham.) Experiments for the 

 control of this disease have been inaugurated with diseased trees of Colorado 

 blue spruce on a private estate in Holyoke and a cemetery in Worcester. The 

 appearance of the trees has been much improved by removal of diseased and dead 

 limbs, and in Holyoke by a summer application of an inorganic fertilizer. The 

 trees in both locations are to be fertilized and sprayed in the spring of 1938. 



DEPARTMENT OF CHEMISTRY 

 W. S. Ritchie in Charge 



Cooperative Analytical Service. (The Department.) Service to outside 

 departments and individuals has been continued. Samples of milk from Harvard 

 Medical School were analyzed for traces of copper with the view of evaluating 

 methods. Thirteen samples of so-called "foreign breads" collected in Boston in 

 connection with the work on diabetes of the Boston City Hospital were analyzed 

 for total carbohydrate. In addition the proximate analysis was determined. 

 The results of the analysis of these breads are expected to be published in a short 

 time. 



Cooperation has continued with the workers at the Waltham Field Station. 

 In particular, certain paint samples (about 18 in number) have been analyzed 

 for soluble zinc and sulfur salts in connection with the "burning" of plants fol- 

 lowing fumigating with sulfur. Details of this work appear in the reports of that 

 group. 



Testing Analytical Methods. (The Department.) The methods for determin- 

 ing iron, copper and manganese, previously reported, have received continued 

 study to the end that they may be made simpler, more accurate, and more rapid. 



Acting as associate referee for methods of determining zinc in small quantities, 

 a method was developed and reported to the Referee on Metals in Foods. By 

 this method the ashed sample is dissolved in 2N hydrochloric acid, since the wet 

 combustion method (sulfuric and nitric acids) was found to be unsuitable. To 

 this acid solution, the carbamate reagent (sodium diethyl dithiocarbamate) and 

 the dithizone (diphenyl thiocarbazone) are added in excess and shaken with 

 carbon tetrachloride. The latter was found to be more agreeable to use than 

 either chloroform or amyl alcohol, solvents sometimes used in this connection. 

 The organic solvent containing some of the interfering metals is discarded and 

 the aqueous solution of the zinc is treated with ammonium citrate, ammonium 

 hydroxide, the carbamate reagent and an excess of dithizone. This is again 

 shaken with carbon tetrachloride, which is washed with dilute (0.02M) ammonium 



.^Published in Plant Disease Reporter 21:3:58-59. Feb. 15, 1937. 



