198 Pflanzenkrankheiten. 



above and perhaps others, are caused by an insufficient supply of 

 available nitrogen, involving in some cases not only nitrogen hunger 

 but internal disturbances in the cells owing to their growth in un- 

 balanced Solutions as media". 



„That the general idea of malnutrition, with respect to nitrogen, 

 of the affected plants in the cases of the diseases above named, 

 may have many phases and the causative agents very widely under 

 different soil and climatic conditions, is indicated by the following 

 possibilities in the direction of an insufficient supply of available 

 nitrogen. 



1. The total nitrogen supply may be very low and hence an 

 insufficient supply of available nitrogen is almost certain to follow. 



2. In soils in which sufficient nitrogen is suppHed the form of 

 the latter may render it unsuitable for transformation to nitrate by 

 flora existent in that soil. 



3. In soils high in carbonates, particularly those of the alkali 

 earths, ammonia may be set free as rapidly as it is formed by the 

 ammonifying bacteria and very little nitrate be produced in those 

 soils as a result. In such cases nitrogen starvation would be expected. 



4. A possibilit}'- which appears of lesser importance in the light 

 of our recent results, is the toxic effect of ammonium Compounds 

 directly assimilated by plants in soils incapable of producing nitrates. 

 In any event, of course, this could only occur in plants which are 

 injured by nitrogen in the form of ammonia". 



The writer suggests the possibility of curing the diseases by 

 direct or indirect soil treatment of a nature to insure a good supply 

 of available nitrogen. In soils poor in humus it would appear to be 

 the best to employ sulfate of ammonia or cottonseed meal, while in 

 soils rieh in humus dried blood and high grade tankage are likely 

 to give better results. It is not expected, moreover, that such treat- 

 ment in the field is likely to be foUowed by quick improvement in 

 the affected plants. The reason for this is that a tree root covers a 

 very large area of soil and it is not possible to influence that large 

 foraging surface of the plants roots quickly. Nevertheless, large 

 applications of the materials named, along with a good water supply 

 and thorough tillage to insure the maximum degree of distribution 

 of the nitrogenous materials should go far to assist and hasten the 

 process of the plants recovery. 



The question may naturally arise as to how one advancing the 

 theory above briefly considered could account for good individual 

 plants or groups of such which are frequently found in the diseased 

 areas. This argument however is erroneous since there is no uni- 

 formity in soils to begin with, but even if this is set aside as of 

 minor importance here, it must be remembered that individuals 

 among plants as well as animals, are frequently more resistant than 

 their fellows to untoward conditions. It is therefore not a valid 

 argument against the theory here promulgated that the soil near 

 good plants as well as that near bad plants in a field is poorly 

 supplied with nitrogen in an available form. 



M. J. Sirks (Haarlem). 



I o 



Lutman, B. F. and H. F. Johnson. Some observations on 

 ordinary beet scab. (Phytopathology. V. p. 30—34. 1915.) 



Beet and potato scab are, as far as the causal organism is con- 

 cerned identical, according Bolley and Arthur and Golden. 



