276 



PRACTICAL COURSE IN BOTANY 



dry, hot, cold, etc. — is also an important 

 factor. In a district open to sea breezes, 

 live oaks, which require a salt atmosphere, 

 maj^ 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 

 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. 



Fig. 413. — A red 

 cedar grown under 

 normal conditions. 



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 neighl^orhood. 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? (309.) 



2. Why is it that plants of the same, or closely related species are found 

 in such different localities as the shores of Lake Superior, the top of Mt. 

 Washington, and the Black Mountains in North Carolina? (311, 330.) 



