AGRICUVrURAI, BOTANY, CHEMISTRY AND PHYSIOLOGY OF PLANTS lOCfy 



wards, the composition of the organic substance of the leaf, and the other 

 two for determining the quantity of humic substance sokible in water and 

 ammonia. Two ammoniacal sokitions were used, one to determine the humic 

 substance insohible in water, and the other to estimate the total quantity 

 of this substance. The determinations were made b}^ the two methods, 

 namely the colorimetric method and the permanganate of potash method. 



The results furnished by each method were compared, and the accuracy 

 of the colorimetric method in particular was shown ; the results of both were 

 to a great degree parallel, but reasons are stated for the preference given to 

 the permanganate method, which enables the work to be done much more 

 rapidly. 



The results of the experiments on maple leaves are combined in the 

 folllowing table. 



Quantitv of humic substances produced in decomposing maple leaves 

 at a constant temperature of ;^j'^ C, when these leaves are incompletely im- 

 pregnated with water. 



Similar results were also obtained with birch leaves, with the difference 

 that the ratio between the proportion of humic substance soluble in water 

 and that soluble in ammonia is not the same as for the maple leaves (being i : i 

 in the latter case, against i : 2 or 3 in the case of the birch leaves). It was 

 also ascertained that a more thorough drjdng of the decomposing leaves 

 entails a reduction in the solubility of the humic matter, and that this is 

 probably the cause of the fluctuations still observed in the table reproduced 

 above. 



Conclusions, i. — The content of water-soluble humic substance varies 

 according to the decomposed leaves ; for instance, for autumn leaves of the 



