268 ANNUAL REPORTS OF DEPARTMENT OF AGRTCULTURE. 



of agriculhiral soils in the regions mentioned and the isolation and 

 correlation of the cellulose-dissolving organisms from different types 

 of soil. During the fiscal year 1013 the relation of cellulose destruc- 

 tion by various types of soil organisms, especially in connection with 

 the utilization of different types of green manures, to crop-producing 

 power will be inx^Bstigated both under greenhouse conditions at 

 Washington and under field conditions at P'allon and other points 

 in the A Vest. 



CROP-PHYSIOLOGY AND BREEDING INVESTIGATIONS. 



The investigations in crop physiology and breeding have been con- 

 tinued during the year under the immediate direction of Mr. Walter 

 T. Swingle, assisted by Prof. S. C. Mason, arboriculturist in charge of 

 dry-land arboricultural investigations; Mr. G. P. Rixford. expert in 

 fig investigations; and Mr. E. M. Savage, assistant plant breeder. 

 They have for their object the determination of the exact climatic, 

 soil, and cultural re((uirementsof important crop ]dants. A study of 

 the factors underlying the physiology of crop production is essential 

 not only for the determination of the best methods of culture and the 

 special treatments demanded to insure success in given localities, but 

 also to determine the direction in which plants can most advanta- 

 geously be modified by the plant breeder. An especial feature of the 

 work has been the search for deep-rooted and drought-resistant tree 

 crops better adapted for culture in the dry-land regions of the United 

 States than the shallow-rooted annual crops now grown. 



Hardy citrus fruits. — This work, which is of great interest to the 

 people living in the cotton belt, has been pushed vigorously during the 

 past j^ear. At present some 5.000 hybrids a year are being made and 

 about 15.000 hybrids are under observation, constituting probably 

 the largest collection of hybrid fruits of definitely known parentage 

 under study in this part of the world. 



At the same time, through the cooperation of the Office of Foreign 

 Seed and Plant Introduction, a number of very hardy types of citrus 

 fruits which promise to give better hybrids than any now under 

 observation have been obtained from Australia, Asia, Africa, and 

 other regions. 



In particular, the Australian desert lime, the hardiest of all the 

 evergreen citrus fruits, is of the greatest promise irf breeding new 

 types. In addition to bearing edible fruits, it is drought resistant 

 and has the very desirable quality of remaining dormant during 

 spells of warm weather in winter. 



It is now clear that some four or five new types of citrus fruits can 

 be produced, covering all of the Cotton States and ranging from 

 Florida to the Ohio and Potomac Eivers. For the regions just out- 

 side the present limits of citrus culture, hardy types of oranges and 

 grape fruit suitable for eating from the hand will undoubtedly be 

 produced, as well as hardy lemons and limes, while for the northern 

 limits there will be deciduous trees bearing small fruits suitable for 

 making ade and for general culinary purj)oses. 



The entire line of this work is proving of such unusual promise 

 that it will be pushed even more vigorously during the coming year 

 than in the past. 



