288 ANNUAL. REPORTS OF DEPARTMENT OF AGRICULTURE. 



in charge of Mr. Karl F. Kellerman, Physiologist. The water-purifi- 

 cation work has consisted chiefly of advisory correspondence, though 

 in some places personal supervision of improvements has been 

 undertaken. 



Work with nodule-forming bacteria. — Pure cultures of nodule- 

 forming bacteria for inoculating legumes have been distributed dur- 

 ing the year and additional data have been gathered concerning the 

 limitations of successful inoculation. Especially with alfalfa in the 

 Eastern States, it has been found that successful inoculation is cor- 

 related very closely with the reaction of the soil to neutral litmus 

 paper. The inoculation of crimson clover seems to show no correla- 

 tion with the litmus reaction, while the inoculation of A'etch is about 

 halfway between these extremes. More detailed field work in connec- 

 tion with the experimental distribution of pure cultures for inoculating 

 legumes will be undertaken during the coming year. 



Studies ix soil bacteriology. — Extensi\e studies regarding the 

 correlation between nitrification and ci'op production have been made 

 in different parts of the United States. It has been found that in cer- 

 tain soils of the Coastal Plain which have a high magnesium content 

 the application of a pure calcium lime, such as oyster-shell lime, is 

 very much more beneficial to the action of nitrifying bacteria than 

 is the application of lime containing a high percentage of magnesium. 

 Investigations carried on chiefly in Utah, Nevada, and Virginia show 

 a very close relationship between the crop-producing power of a soil 

 and the development of nitrifying bacteria in that soil. These in- 

 vestigations will be extended to cover more types of soil organisms, 

 and, where possible, field work in cooperation with other offices of the 

 Bureau will be undertaken. It is also planned to make a general sur- 

 vey of the bacterial conditions obtaining throughout various parts of 

 the United States. 



CROP PHYSIOLOGY AND BREEDING INVESTIGATIONS, 



Investigations concerned primarily with the determination of the 

 factors underlying the physiology of crop production have been con- 

 tinued under the immediate supervision of Mr. AValter T. Swingle, 

 Physiologist, assisted by Prof. S. C. Mason, Arboriculturist in Charge 

 of Dry-Land Arboricultural Investigations, 



Breeding hardy types of citrus fruits. — The hardy hybrids 

 obtained by crossing the common orange with the trifoliate orange of 

 Japan and China liave yielded a consideral)le number of new citrus 

 vai'ieties suitable for culture throughout the Cotton States. Some 

 thousands of grafted plants of half a dozen of the best varieties of 

 these citranges, as they are called, have been distributed in the cotton 

 regions and many favorable reports have been obtained from the 

 growers. The work has been extended during the past two years, 

 more than 10.000 crosses having been made in the spring of 1909 

 by Mr. Swingle in Florida and by Mr. E. M. Savage, Assistant, in 

 California. Many of these are complex hybrids — that is, the citranges, 

 themselves of hybrid origin, have been crossed with various other 

 citrus fruits in the hope of obtaining hybrid forms which contain only 

 a small proportion of the blood of trifoliata and which could be rea- 



