THE FOOD OF PLANTS. 



91 



retains in solution small quantities of certain humous substances. 

 If we collect the Humic acid on a filter, wash well with water, 

 and dry, we get a brittle, crumbling black mass, which is almost 

 insoluble in water. If, on the other hand, still moist Humic 

 acid is treated with water, somewhat larger quantities of the 

 substance pass into solution. This solution of Humic acid has 

 a yellowish brown colour. If we add Humic acid to solution of 

 ammonia, it readily dissolves with formation of Ammonium 

 humate. If we add to this solution a solution of Calcium chloride, 

 a precipitate is produced consisting of the double humate of 

 Calcium and Ammonium, a compound which can also undoubtedly 

 be formed under some conditions in nature. The soil certainly 

 contains in addition a whole series of other humous compounds, 

 about which, however, nothing is accurately known. 



FIG. 25. Beech root grown in unsterilised 

 wood humus : p, strands of fungal hypha?, 



FIG. 26. Beech root grown in wood 

 humus freed from fungus by sterilisation. 

 It is not provided with fungal hyphse, and 

 has root hairs h. At c is the root tip with 



at a associated with humus. Magnified its root cap. Several times magnified, 

 several times. (After Frank.) (After Frank.) 



We carefully pull up from the humous soil of a wood a young 

 beech plant (Fagus sylvatica), and convey it, wrapped in moist 

 moss, into the laboratory. After washing the root with water, 

 we perceive fine root fibres to which cling small fragments of 

 humus. These fibres we cut off, let them lie in water for a 

 time to soften the humus, and then examine them under slight 

 magnification. Hoot hairs are absent. Instead of that, the entire 

 surface of the fibres is covered with a tissue of fungal hypha3. 

 From the root fibres also radiate in all directions fine hyphee and 

 thick hyphal strands, to which frequently fragments of humus cling 

 (see Fig. 25). Here we have to do with Mycorhiza, 1 au,d 



