226 HANDBOOK OF NATURE STUDY 



old spoon, and then put the spoon on a strong coal fire and 

 left it there for about half an hour ; at the end of that time 

 the black color of the soil had disappeared. As I have 

 often observed that decayed logs and leaves in the woods 

 form a dark mould, I concluded that the dark color in the 

 surface soil is due to decayed and finely divided vegetable 

 matter, and that the dark color of the soil disappeared be- 

 cause this vegetable matter had been burned." 



Fred's conclusion is correct, and I wish more of you would 

 perform the same experiment. We find, then, that the prin- 

 cipal constituents of agricultural soil are sand, clay, and vege- 

 table mould or humus. Besides these the soil contains small 

 quantities of several other substances, such as potash, soda, 

 lime, common salt, and iron. If you bleach out a little 

 ashes, you can taste the potash and soda in the lye, because 

 they are easily soluble. Only such minerals as dissolve in 

 water can be absorbed by plants. 



The best soil for plant growth, and therefore for farming 

 and gardening, is a black loam. Loam is a mixture of clay, 

 sand, and humus. Very sandy soil is too porous, and lets 

 the rain water pass through too quickly, and on that account 

 crops are likely to fail on it unless frequent rains occur. 

 Clay is, in this respect, the very opposite of sand. It is 

 sticky, quite impervious to water, and therefore holds the 

 surface water too long in a rainy season, but becomes baked 

 and hard in a dry season. Black loam, however, has just 

 the right porosity for plant roots and for drainage, and still 

 holds a sufficient amount of water and air. On account of 

 its dark color it absorbs the rays of the sun and makes a 

 much warmer soil than clay. For these reasons it is the best 

 soil for a large majority of plants. 



The crumbling stones which I have here, and the fact 

 that even hard building stones wear and weather if ex- 

 posed to the atmosphere, to rains, heat, and frost, is evi- 



