REPORT OF THE SECRETARY. 139 



tomato wilt and rot, a number of ginseng diseases, and the whole 

 group of nematode diseases have been studied critically and control 

 measures introduced. 



Leaf-spot and curly-top, two important diseases of sugar beets, 

 have been thoroughly investigated, and better methods for combating 

 them have been pointed out. Similar work has been done in con- 

 nection with the damping-off and toot-rot of sugar beets. 



SOIL-BACTFBIOLOGY AND PLANT-NUTRITION INVESTIGATIONS. 



Satisfactory methods for isolating and distributing nitrogen-fixing 

 bacteria for improving leguminous crops by inoculating the seed or 

 the soil were discovered. Tests in cooperation with thousands of 

 farmers throughout the United States have shown that such crops 

 as clover, alfalfa, vetch, peas, and beans are often doubled or trebled 

 in value by pure-culture inoculation. During the past five years the 

 efficiency of the cultures distributed to farmers has been approxi- 

 mately 75 per cent. 



The copper-sulphate method for destroying objectionable algae 

 in city water supplies without lowering the safety of the supply has 

 been discovered and practically demonstrated. This method has 

 become standard practice in sanitary engineering and is recommended 

 by the leading sauitary experts. It was found that copper sulphate 

 could be used in water supplies as an agent for killing dangerous 

 germs, such as those causing cholera and typhoid. Simple directions 

 for improving farm water supplies have also been formulated. 



Extensive bacteriological studies to explain the variation in soil 

 fertility have been undertaken, and during the past year the classical 

 ideas regarding the decomposition of cellulose, which is considered 

 a fundamental substance in humus formation, have been found to 

 be erroneous. j\Iany new and important species of soil bacteria that 

 dissolve cellulose are under investigation, which are expected to 

 make possible more suitable farm practices for maintaining soil 

 humus. 



WORK ON DRUG PLANTS. 



It has been shown that numy valuable drug and related crops can 

 be successfully grown in favorable regions throughout the country. 

 The culture of golden-seal and paprika peppers has been success- 

 fully established. Camphor culture has been introduced in Florida, 

 with results sufficiently promising to attract private capital on an 

 extensive scale. 



The culture of American tea has been introduced in a demonstra- 

 tion oxpi>rinient now yielding an annual crop of 14,000 to lO.OOO 

 pounds of high-grade tea, all of which finds a ready market in com- 

 petition with imported teas. 



