BUREAU OF PLANT INDUSTRY. 279 



Cotton and Truck-Crop Diseases and Sugar-Plant Investigations this 

 office has been studying certain physiological factors affecting cabbage 

 and spinach under conditions frequently found in trucking regions, 

 and suggestive results have been obtained. In cooperation with the 

 same office the curly-top of sugar beets has received some attention, 

 especially from the standpoint of photosynthetic and respiratory 

 functions. It is hoped that with a better understanding of the physi- 

 ological processes underlying these diseases effective preventive meas- 

 ures may be devised. 



The laboratory study of the physiological significance to plants of 

 certain chemical substances in dilute solutions has been continued. 

 It is clear that the normal behavior of the crops mentioned and 

 others is to a considerable extent influenced by the properly con- 

 stituted supply of inorganic salts in proper concentration. The ques- 

 tion, therefore, of the effect of dilute solutions of these salts on these 

 crops is a vital one. Accordingly, during the past year the effects of 

 dilute solutions bearing in minute proportions the most important 

 inorganic salts have been studied in their relation to beets, peas, and 

 other truck crops. It has been demonstrated that calcium and mag- 

 nesium in extreme dilution are very important constituents in secur- 

 ing the health of the crop. It appears, moreover, that not only are 

 these substances necessary through the quantities wliich are present, 

 but also through the relation which these substances bear to each 

 other. It appears that the function of iibsorption is affected by one 

 ratio, but the general development of the plant is dependent on a 

 somewhat different ratio. It is hoped that through the employment 

 of some novel and refined methods in this line of laboratory inves- 

 tigation information of great physiological and economic impor- 

 tance may be obtained and that the results will be capable of general 

 application. 



Fermentation investigations. — The work of fermentation investi- 

 gations during the past year has been confined chiefly to a study uf 

 the action of certain so-called oxidizing ferments, or enzymes, which 

 bring about important changes in many technical products. It 

 appears that these ferments are closely related to processes of respira- 

 tion and are more or less closely connected with the development of 

 plant pigments and other classes of products having commercial 

 significance. Conspicuous in this line are such fermented products as 

 black tea and vanilla pods as they appear on the market. These 

 oxidizing enzymes are also likely under various conditions to produce 

 a harmful action, as in the case of certain vegetable drugs which 

 when exposed to the air deteriorate in value. An accurate method 

 of measuring the activity of these ferments has long been wanted, 

 and during the past year such a method has been worked out and is 

 now being applied to practical technical problems. 



PLANS FOR FUTURE WORK. 



As the problems of the office largely consist of investigations requir- 

 ino- considerable time, work will be continued along the present lines. 



Drug plants and other special crops. — The usefulness of the 

 small experimental cultures at the various testing gardens is being 

 demonstrated in the results obtained, which have led to the expansion 



