102 NATURE AND PROPEETIBS OF SOILS 



constitution. Simple proteins, such as albumin, globulin, pro- 

 tamins, and others, are found in plants, besides certain de- 

 rived proteins sucii as proteosis and peptones. In addition 

 to all these, there is a host of other nitrogenous compounds 

 that have no small influence on the composition of the soil 

 organic matter.^ 



It is also necessary to consider that certain portions of the 

 cell contents and cell walls are in a collodial state. Such a 

 condition is important as the translocation of dissolved sub- 

 stances from soil to plant and from cell to cell depend largely 

 on their diffusibility through colloidal membranes. 



It is evident even from this brief discussion that the chem- 

 ical character of plant tissue is far from simple. The degra- 

 dation of such material, especially in the presence of com- 

 plex mineral products, generally gives rise at first to com- 

 pounds no simpler; in fact, the chances are that the result- 

 ing compounds will be much more complicated. It is only 

 later in the processes of decomposition that simple products 

 result. 



* Crops are usuaUy analyzed for six constituents — water, ash, crude 

 protein, crude fiber, nitrogen fiee extract, and crude fat. Water is 

 determined by drying the sample at the temperature of boiling water. 

 By burning a sample of the plant tissue until all of the organic matter 

 has been driven off, the percentage of mineral matter may be found. 

 Crude protein is obtained by mulptiplying the figure for total nitrogen 

 by 6.25. Crude fat is found by extracting the dry plant tissue with 

 ether, while the crude fiber is that which remains of the fat-free material 

 after treatment with both dilute sulfuric acid and dilute sodium hydrox- 

 ide solutions. Nitrogen-free extract is the difference between the sum 

 of the above constituents and 100 per cent. Below are four typical 

 analyses: 



Crop 



Water 

 % 



Ash 



% 



Crude 



proteiisi 



% 



Crude 

 Fiber 



% 



Nitrogen 



Free 



Extract 



% 



Crude 



Fat 



% 



Alfalfa (green) . . . 

 Lettuce (fresh) . . . 



Wheat (grain) 



Timothy (hay) . . . . 



71.8 

 94.7 

 10.5 

 13.2 



2.7 



.9 



1.8 



4.4 



4.8 



1.2 



11.9 



5.9 



7.4 



.7 



1.8 



29.0 



12.3 



2.2 



71.9 



45.0 



1.0 



.3 



2.1 



2.5 



