ELEMENTS OF AGRICULTURE. 
4S 
8. In what circumstances is turf sour ’ 
9. What distinction is drawn in the value of humus T 
10. Which is the best humus, that derived from animal or that SiPuSB 
vegetable matters ? 
11. In which case is humus sour ? 
12. What means are employed to correct the acidity in humus ? 
13. In what does paring and burning consist 1 
14. What other advantage does this mode possess ? 
LESSON IX. 
OF THE ACTION OF HUMUS IN THE SOIL. 
63. Organic remains that are decomposed in the soil 
produce two different effects: 1. They furnish the plants 
with a part of their nutritive principles. 2. They act 
upon the physical properties of the soil. 
64. The properties of the soil are divided into two 
classes. Those that relate to its composition take the 
name of chemical properties; and those that concern its 
texture, its position, etc., are called physical properties. 
65. The action of humus, as food for plants, has been 
very much discussed by modern writers. Some contend 
that humus, by means of the carbon that it contains, fur¬ 
nishes the roots with the greater part of the elements 
necessary to the vegetation of the plant; and that a feeble 
portion only of these elements is derived from the atmo¬ 
sphere. Others, on the contrary, have maintained that the 
atmosphere supplies the greater part of the nutritive ele¬ 
ments, because the hydrogen, oxygen, and carbon, that 
enter into the composition of all vegetables, are furnished 
y air and water, and are consequently derived from the 
atmosphere. 
66. This last opinion is in truth supported by some facts 
Thus, we have some very productive lands eontaining.very 
little humus. Some vegetables, supplied with water only, 
