JOMAL OF AGRICILTIAL RESEARCH 



Vol. XV Washington, D. C, November i8, 1918 No. 7 



PHYSIOLOGICAL STUDIES OF NORMAL AND 

 BLIGHTED SPINACH^ 



By Rodney H. True, Otis F. Black, James W. Kelly, H. H. Bunzell, Lon A. 

 Hawkins, Samuel L. Jodidi, and Edward H. Kellogg, Drug-Plant, Poisonous- 

 Plant, Physiological, and Fermentation Investigations, Bureau of Plant Industry, 

 United States Department of Agriculture 



INTRODUCTORY STATEMENT 



For some years the growing of spinach {Spinacia oleracea) in the truck- 

 ing sections of Norfolk, Virginia, has been seriously affected by a disease 

 known as "spinach-blight," which is marked by a dwarfing of the 

 affected plants, with a change of color from dark to yellowish green, and 

 the development of a sweet taste and bitterness when the leaf is folded, 

 similar to that seen in a mature tobacco leaf. 



This disease has been shown by McClintock and Smith (29)^ to belong 

 to the "mosaic" group. It is therefore a "virus disease" readily com- 

 municable from blighted to healthy plants by contact, by injection of 

 plant extracts, and especially by aphids. These insects are responsible 

 for the rapid spread of the disease in the field. 



Earlier work by Harter (16) and others on the malnutrition of truck 

 crops has led to the belief that this spinach trouble was attributable to 

 the lack of lime and humus, with excessive acidity of the soil, and the 

 work reported in these papers was begun in the hope of throwing light 

 on the abnormal physiological reactions observed. In carrying out these 

 plans, laboratory investigations were made of the ash, carbohydrate, 

 and oxidase contents of both normal and blighted plants, as well as a 

 more fundamental study of the nitrogen metabolism. 



Since the nutrition of the plants is closely connected with the condition 

 of the soil in which they grow, and since it has been suggested that the 

 occurrence of the disease might in some degree be influenced by soil con- 

 ditions {16, 17), it was deemed necessary to take these possible factors 

 into account. The results of an examination of field conditions by Dr. 



1 The investigations here presented bear on different phases of the same problem, although carried out 

 by different workers. Since different men are responsible for the results presented, requiring as they do 

 different types of technic and different lines of special interest, the results are presented in separate chap- 

 ters in which both the responsibility and the credit of authorship are separately indicated. 



2 Reference is made by number (italic) to " Literature cited," pp. 405-408. 



Journal of Agricultural Research, Vol. XV, No. 7 



Washington, D. C. Nov. 18, 1918 



qe Key No. G-i6a 



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