436 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



available for taking up investigations in the dark fire-cured district 

 of Tennessee, with headqiuirters at Clarksville. The work at that 

 point will be along the same lines that are followed at Hopkinsville, 

 Ky., including the development of pure strains of the best standard 

 varieties, a study of the fertilizer requirements of the tobacco crop, 

 and systems of rotation specially adapted to tobacco culture. 



PLANT-lSrUTRITION INVESTIGATIONS. 



The investigations of plant nutrition in charge of Dr. W. W. 

 Garner have to do with special problems of a broad nature, not per- 

 taining primarily to any particular crop plant. The principal fea- 

 ture of the work now in progress relates to a quantitative study of 

 the comparative effects of some of the principal factors of nutrition 

 on the growth and development of plants. The work includes labora- 

 tory, greenhouse, and field studies, and the facilities at the Arlington 

 farm are largely utilized in obtaining material for experimentation. 



Relation of nutrition to the composition of plants. — The in- 

 vestigations in progress deal with the oil content of crop plants as 

 affected by nutrition. The more general features of the work have 

 been largely completed and will soon be ready for publication, but 

 additional data are yet to be gathered as to the relative influence of 

 some of the primary factors of nutrition, considered singly, on the 

 formation of oil in the plant. The data already obtained are based 

 on studies of soy beans, cotton, peanuts, and flax. 



Leaf developiment as affected by nutrition. — A study of the 

 effects of the principal factors of nutrition on the physical characters, 

 such as size, shape, and thickness, has been undertaken. Inasmuch 

 as the structure and composition of the leaf of tobacco are known 

 to be readily influenced in these particulars, this plant has been 

 used in the investigations. * Very striking results have already been 

 obtained. 



ALKALI AND DROUGHT RESISTANT PLANT BREEDING. 



The breeding and physiological investigations of plants in rela- 

 tion to alkali and drought have been continued in the arid and semi- 

 arid portions of the United States under the direction of Mr. T. H. 

 Kearney. 



Breeding for drought resistance. — The object of the breeding 

 work in charge of Mr. A. C. Dillman is to develop profitable varieties 

 of crop plants possessing the greatest abilit}^ to withstand drought. 

 Improved strains of alfalfa, sorgo, millet, and awnless brome-grass, 

 well adapted to dry farming in the northern and central portions 

 of the Great Plains, have already been developed. These strains are 

 being compared in order to ascertain which strain of each crop is 

 best adapted to withstand drought. Pending the rasults of these 

 tests, seed of the strains of known superiority is being increased for 

 distribution. 



Physiology of alkali and drought resistance. — Cooperative in- 

 vestigations in charge of Dr. H. L. Shantz relate to the ratio of water 

 used to weight of dry matter produced by plants. Many crop species 



