404 Journal of Agricultural Research voi. xv, no. 7 



As will be seen by reference to Table VIII, column 12, the percentage 

 of peptid nitrogen is usually higher in the healthy tissues than in the 

 diseased tissues. 



The diseased spinach collected in May, 191 6, is strikingly different from 

 the diseased spinach gathered in December, 191 5, and January, 191 6, 

 An examination of Table VIII shows that the percentage of nitrogen in 

 the form of acid amids and basic nitrogen is smaller in the former than in 

 the latter. This, together with the fact that the protein nitrogen of the 

 May sample is higher than that of the December and January samples 

 (see Table IV) points to the former as being in a riper state whereby the 

 acid amids and basic-nitrogen compounds have preferably been used by 

 the plant for building up protein substance. 



The results for residual soluble nitrogen in which the different fluctua- 

 tions of the various constituents (ammoniacal nitrogen, acid amid nitro- 

 gen, etc.) are reflected, range from 10 to 17 per cent in the case of the 

 healthy spinach, and from 15 to 19 per cent in the case of the diseased 

 materials. The May sample has as much as 27 per cent, calculated on 

 the total soluble nitrogen. 



SUMMARY 



(i) It has been shown (p. 381-384) that carbohydrates accumulate in 

 the leaves of plants affected with the spinach-blight in considerably 

 greater quantity than in normal leaves. 



(2) In this paper it is shown that the accumulation is not due to the 

 inability of the diseased plants to make proteins. Although these con- 

 stituents are found in the tops of the diseased plants in a somewhat 

 smaller percentage calculated on the dry weight of the material than in 

 the normal tops, the proteins make up a larger proportion of the total 

 nitrogen in the diseased than in the healthy material. The proteins in 

 the roots of diseased plants exceed those found in the roots of normal 

 plants, both in reference to the dry weight of the material and to the 

 total nitrogen. 



(3) Spinach -blight is physiologically characterized by retarded growth, 

 and a lower moisture content. This seems to be due to the fact that 

 the rapidly growing normal tissues are comparatively rich in water and 

 poor in complex organic compounds, such as proteins, etc. 



(4) The lower percentage of total nitrogen and of acid amid nitrogen 

 in the diseased material can best be explained by the assumption that 

 denitrification takes place in those tissues, whereby a part of the nitrogen 

 may be lost either as elementary nitrogen or in the form of ammonia. 



(5) The reason for the higher proportion of ammoniacal nitrogen in 

 the diseased material than in the corresponding healthy tissues would 

 be sought in the processes of denitrification, whereby a part of the ni- 

 trites is further reduced to ammonia. 



