ORGANIC CONSTITUENTS OF SOILS. 15 



guanidine will grow nicely for three or four days without any pecu- 

 liarity being noticeable in either group. The cultures higli in nitrates 

 will be the first to show the symptoms of guanidine poisoning, and 

 this effect will spread through the guanidine group of cultures, be- 

 coming more and more marked in those high in nitrates. At the 

 conclusion of two weeks the group of cultures containing no guanidine 

 will appear green and fresh, whereas the guanidine group appears 

 bleached and wilted in all of the cultures containing nitrates. The 

 cultures which contain no nitrate that is, only potash and phosphate 

 are the only cultures which have been able to withstand the ravages 

 of this poisonous compound. We have here not only a striking 

 illustration of the harmful effect of an organic nitrogenous com- 

 pound, but also an example of the increased harmful effect brought 

 about by the addition of the otherwise beneficial nitrate. This is in 

 striking contrast to the ameliorating effect of nitrates over all other 

 fertilizers in the case of the harmful soil constituent, dihydroxy- 

 stearic acid. Guanidine is harmful, and dihydroxystearic acid is 

 harmful, although this manifests itself in a different way. Nitrate 

 increases the harmfulness of guanidine, but decreases the harmful- 

 ness of dihydroxystearic acid. Here is an effect of a fertilizer which 

 is entirely unexplainable from the viewpoint of mineral require- 

 ment or plant-food addition. 



This is not the only illustration of a differential action of a. fer- 

 tilizer salt. Nor is this behavior of nitrate in influencing the effect 

 of these organic substances on plant growth and development the 

 only illustration of the influence that different fertilizer salts exert 

 on this action of the organic compounds. Cumarin is another 

 substance which we have studied quite thoroughly in its effect on 

 wheat seedlings. Besides decreasing growth, it also has a very 

 peculiar and characteristic action on plants which enables the ex- 

 perimenter to pick out cumarin-affected plants at a glance from 

 those affected by any other toxic body studied by us. The leaves 

 arc shorter and broader than is normal for wheat, and only the first 

 leaves are usually unfolded, the other leaves remaining wholly or 

 partially within the swollen sheath. Such leaves as do break forth 

 are usually distorted and curled or twisted. Now, when cumarin is 

 contained in the cultures containing the various fertilizer salts it is 

 quite apparent that neither nitrate nor potash affect these charac- 

 teristic symptoms of cumarin poisoning, but the slightest addition 

 of phosphate causes a very decided change in the appearance of the 

 plants. This increases with increasing phosphate until nearly normal 

 development is obtained, as shown by comparison with the corre- 

 sponding cultures without cumarin. 



I must also cite to you the influence of quinone when similarly 

 studied. The effect of quinone is decidedly different from the effect 



