THE ROOT 71 



sorption, roots must have access to a suitable soil. To pro- 

 duce the best results a soil must contain (1) all the essential 

 mineral constituents (62) ; (2) moisture for dissolving these 

 materials ; and (3) air enough to supply the oxygen which is 

 necessary to the life processes of all green plants. 



75. Composition of soils. Sand, clay, and humus, or 

 vegetable mold, with the various substances dissolved in 

 them, constitute the basis of cultivated soils. A mixture 

 of sand, clay, and humus is called loam. When the propor- 

 tion of humus is very large and well decomposed, the mixture 

 is called muck. Pure sand contains but little nourishing 

 matter and is too porous to retain water well. Pure clay 

 is too compact to be easily permeable to either air or water. 

 Most soils are composed of a mixture of the two with vege- 

 table mold in varying proportions, giving a sandy loam, or 

 a clay loam, as the case may be. 



76. Tillage. -- The advantages of tillage are: (a) that by 

 breaking up the hard lumps it renders the soil more per- 

 meable to air and water and more easily penetrable by the 

 roots in their search for food ; (b) the covering of loose, 

 friable earth left by the plow and the harrow acts as a mulch, 

 and by shading the soil below, prevents too rapid a loss of 

 water by evaporation. Where the essential food ingredients 

 are present, good tillage counts for more in making a crop 

 than the original quality of the soil. 



77. Light and heavy soils. - - These terms are used by 

 farmers not in relation to the weight of soils, but in reference 

 to the ease or difficulty with which they are worked. Light 

 soils contain a preponderance of sand ; heavy ones, of clay. 



Practical Questions 



1, Will plants grow better in an earthen pot or a wooden box than 

 in a vessel of glass or metal? Why? (Exp. 46.) 



2. Which absorb more from the soil, plants with light roots and abun- 

 dant foliage, or those with heavy roots and scant foliage ? (Suggestion: 

 roots absorb from the soil ; leaves, mainly from the air.) 



