FERTILIZERS. 285 



dilute solution of liumate of liine, and (3) ordinary water. The plant- 

 lets grown in the huniate solution developed much more rapidly than 

 those grown in either of the other solutions. To get still more positive 

 evidence of the assimilation of humus by plants a tuft of Poa annua 

 was extracted from the soil, the roots cut off, and the tuft placed in 

 water until new white roots had developed. The tuft was then divided 

 into two i^arts, from one of which the upper part of tlie plant was 

 removed. Each part was placed in a highly colored sohition of liumate 

 of potash. After 2 days the humus had almost entirely disappeared 

 in the solution in which the^ roots with tops attached had been placed, 

 while the solution in which the detached roots had been placed was 

 apparently unaltered. 



The experiments of Sachs, in which tracings were obtained on 

 marble by the action of the roots of bean plants, were repeated with a 

 tuft of Poaj substituting a piece of filter paper covered with humic 

 acid for the marble slab. The tracings which Sachs obtained were 

 reproduced on the black layer of humus. 



It IS a well-known fact that when the soil in which plants are grow- 

 ing IS abundantly supplied with jilant food the roots remain short and 

 tliick, while in poor soils they spread out to a great distance. A tuft 

 of Poa, pro-vided with aquatic roots produced as described above, was 

 suspended between two flasks, one half of the roots hanging in one 

 flask containing water to which 1 gm. of phosphate of potash per liter 

 had been added, and the other half in the second flask containing 

 water to which had been added, in addition to the above proportion of 

 phosphate of potash, sufficient humate of potash to render the solu- 

 tion brown. At the end of 2 creeks the roots in the flask without 

 organic matter had attained twice the length of those in the other 

 flask. 



Experiments with humate of soda gave the same results as those 

 with humate of potash. Other experiments showed that the Poa 

 l)lants assimilated sugar with great rapidity when their roots were 

 immersed in a solution of this substance. 



These experiments seem to warrant the conclusion that plants are 

 able to absorb carbonaceous organic substances through their roots, 

 and that they derive great benefit from this supply of plant food. 



The doubt which has been cast upon the ability of plants to directly 

 absorb and assimilate the organic matter of the soil would appear to 

 be dispelled by the results liere reported. 



Intensive culture with chemical fertilizers is the cause of a serious 

 loss of organic matter in the soil. Deherain, who has shown that the 

 fertility of a soil declines as the humus content decreases, has called 

 attention to the danger from this source. At the same time he has 

 proposed a remedy, viz, the culture of catch crops to prevent the oxi- 

 dation of humus and loss by drainage and to furnish in autumn a mass 

 of vegetable matter to be turned in as green manure. 



