16 ORGANIC CONSTITUENTS OF SOILS. 



of cumarin, which produces short, broad, irregularly developed 

 leaves and stunted tops; the effect of quinone is to produce long, 

 thin leaves and tall, slender plants. The interesting part in this 

 connection, however, lies in the fact that the growth in the cultures 

 high in potash was nearer to the normal than the growth in either 

 the mainly phosphatic or mainly nitrogenous cultures and was, in fact, 

 poorest in the latter. Vanillin similarly studied behaved like the 

 dihydroxystearic acid, in that nitrates were the most efficient aid to 

 counteract its harmful effect on plants. These experimental facts 

 present much interesting material for discussion from various points 

 of view, but I wish here only to call your attention to the relations 

 between organic compounds, their effect on plants, and the action 

 of fertilizers in this connection, which action is apparently apart and 

 in addition to any food value of the fertilizer salts for plants in the 

 usually accepted sense. In the illustrations which I have given you 

 it is clear, then, that the various fertilizer salts acted differently in 

 overcoming the respective harmful effects of these toxic organic com- 

 pounds. The mainly phosphatic fertilizers were the most efficient 

 in overcoming cumarin effects; the mainly nitrogenous fertilizers, in 

 overcoming the vanillin and dihydroxystearic acid effects ; the mainly 

 potassic, in overcoming the quinone effects; and, in the case of 

 guanidine, the mainly nitrogenous fertilizers even had the effect of 

 increasing the harmfulness of this compound. It is clear that the 

 organic compounds in soils, whether already isolated and studied or 

 yet to be found, are potent factors in soil fertility, as they have a 

 direct effect on plant growth and plant metabolism and on the 

 action of fertilizers. These actions of the different fertilizer combi- 

 nations, or different fertilizer requirements, as they may be styled, 

 show a certain parallelism with field observations on soils and their 

 fertilizer requirements, and one is tempted to ask to what extent 

 the different fertilizer requirements of different soils, or of the same 

 soil under different conditions, may be influenced by the same cause. 

 That harmful bodies occur in soils has been amply shown, and that 

 these are influenced directly or indirectly by fertilizer salts is also 

 clear from this and other researches. That the constitution of the 

 organic matter varies from soil to soil and in the same soil under 

 different conditions of aeration, drainage, and cropping is likewise 

 clear. The presence of compounds inimical to plant growth by virtue 

 of a property resembling that of any of the above mentioned sub- 

 stances might, therefore, cause a different fertilizer requirement, a 

 requirement which might even change from time to time, according 

 to the nature of the biochemical relations producing the compound 

 or according to the nature of the plant remains in the soil; in other 

 words, according to the rotation with its necessary altered soil man- 



