ELEMENTS OP AGRICULTURE. 
45 
thoroughly acquainted with the exhausting power of the 
plants that he cultivates, so as not to exact from the 
land more than it can yield. We shall return to this sub¬ 
ject hereafter. 
53. All organic bodies are not composed alike, nor are 
they of equal value as manures. They may be derived 
from vegetables or animals. Those of vegetable origin are 
formed for the most part of oxygen, hydrogen, and carbon. # 
There are a few vegetables, such as the cabbage and rape, 
that contain azote.f Animal remains, on the contrary, all 
contain azote, united to the three other bodies; and for 
this reason they are more nourishing, more active,, but less 
durable, than vegetable substances, because they are de¬ 
composed more rapidly. 
54. All organized bodies are not decomposed with equal 
rapidity. In the vegetable, as in the animal kingdom, 
there are some that remain a long time in the soil, without 
producing the least effect. Different means are employed 
to render them suitable to the wants of vegetation, as we 
shall see in the following lesson, treating of humus. 
QUESTIONS. 
1. What must be done to make a soil productive ? 
2. Do organic bodies always retain the same form ? 
3. Is vegetation the source of reproduction ? 
4. What is it that renders the soil rich and productive T 
5. What vegetables ought to be cultivated upon a poor soil ? 
6 . What are the remains that certain vegetables leave in the soil ? 
7. Do all plants exhaust the soil 1 
8. Are all organized bodies formed of the same elements ? 
9. Of what elements are vegetables formed ? 
10. What elements form animals ? 
11. Do all organic remains decompose with equal rapidity ? 
* Hydrogen and carbon are two bodies very generally disseminated 
throughout nature. Hydrogen united with oxygen forms water. Carbon 
is nothing more than pure charcoal. Plants assimilate to themselves a 
greater quantity of this substance than of any other. 
t Azote is a body which, united with oxygen, forms the air that we breathe 
