276 PRACTICAL COURSE IN BOTANY 
dry, hot, cold, ete.—is also an important 
factor. In a district open to sea breezes, 
live oaks, which require a salt atmosphere, 
may sometimes be found as far as a hun- 
dred miles from the coast. 
315. Soil.— While water is the most im- 
portant, soil is perhaps the most interesting 
of these factors to the farmer, because it is 
the one that he has it most largely in his 
power to modify. It is to be viewed under 
two aspects: first, as to its mechanical prop- 
erties, whether soft, hard, compact, porous, 
light, heavy, etc. ; secondly, as to its chemical 
Fig. 413.— A red 
cedar grown under ene 
normal conditions. composition and the amount of plant food- 
materials contained in it. The first can be 
regulated by tillage and drainage, the second by a proper 
use of fertilizers. 
EXPERIMENT 92. To SHOW THE INFLUENCE OF SOIL AS AN ECOLOGICAL 
Factor. — Fill a number of small earthen pots with all the different kinds 
of soil that are to be found in your neighborhood. Keep well moistened 
and make a list of the plants that appear spontaneously in each. Is 
there any difference in the kinds produced by different soils? In vigor 
or abundance of the same or different kinds? Do more seedlings appear 
in any of the pots than could live if left alone? What becomes of a ma- 
jority of the seedlings that come up in a state of nature? 
After a time, stop watering until all the plants are dead and new ones 
cease to appear. Notice the rate at which vegetation dies out in each 
and the kind of plants that can live longest without water. Which of the 
different soils is capable of sustaining vegetation longest without a fresh 
supply of moisture? To what quality of the soil is this due? (Exp. 53.) 
Practical Questions 
1. Is the relation between man and the plants cultivated by him a 
symbiosis? (809.) 
2. Why is it that plants of the same, or closely related species are found 
in such different localities as the shores of Lake Supcrior, the top of Mt. 
Washington, and the Black Mountains in North Carolina? (811, 330.) 
