26 abstracts: plant physiology, phytopathology 



that better results would be obtained in rooms constructed of earth, 

 bricks, or concrete than in rooms of wooden or metal construction. 



, R. H. T. 



PLANT PHYSIOLOGY. — ■Absorption and excretion of salts by roots, 

 as influenced by concentratiori and composition of culture solutions. 

 I. Concentration relations of dilute solutions of calcium and mag- 

 nesium nitrate to pea roots. R. H. True and Hi H. Bartlett. 

 Bulletin 231, Bureau of Plant Industry, U. S. Department of 

 Agriculture. Issued January 30, 1912, 

 Secondary roots of the pea will not develop in m/5000 Mg (N03)2. 

 A calcium to magnesium ratio of 1/10 is the lowest ratio at which cal- 

 cium entirely inhibits the harmful effect of magnesium in solutions of 

 this concentration. In solutions of such concentration that magnesium 

 alone would not prevent the formation of secondary roots (e. g., m/20,- 

 000) the calcium to magnesium ratio which brings about perfect root 

 development is nearer 1/100. In solutions of whatever concentration 

 the calcium to magnesium ratio most favorable to absorption of salts 

 is 1/1. 



For calcium nitrate solution used as a culture medium, or for mag- 

 nesium nitrate solution, or for mixtures of the two in any ratio, there is 

 a definite concentration above which roots absorb more electrolytes than 

 they excrete and below which they excrete more thany they absorb. 

 This equilibrium concentration is 12 m/500,000 for Mg (N03)2 and 

 7 m/50,000 for Ca (N03)2. For solutions of the two in the lowest ratio 

 which permits perfect root development (Ca: Mg: : 1 : 10) the equilib- 

 rium concentration is 8 w/500,000, almost as low as for Ca(N03)2 alone. 

 For solutions mixed in the most favorable ratio for absorption (i. e., 

 5/5) the equihbrium concentration is 5 w/500,000, lower than for Ca- 

 (N03)2 alone. H. H. B. 



PHYTOPATHOLOGY.— r/?c history and cause of the coconut bud-rot. 

 John R. Johnston. Bulletin No. 228, Bureau of Plant Industry, 

 U. S. Department of Agriculture. Pp. 175, pis. 14 and figs. 10. 

 February, 1912. 

 Bud-rot is a disease of coconuts which has been known for more than 

 thirty years in Cuba, causing widespread loss. A similar trouble has 

 existed for years in Jamaica, British Honduras, Trinidad, and British 

 Guiana. It is reported also in British India, German East Africa, Por- 

 tuguese East Africa, the Philippines, and Ceylon. 



