240 ECOLOGY 



a salt atmosphere, may sometimes be found as far as a 

 hundred miles from the coast. 



346. Soil is perhaps the most interesting of these fac- 

 tors 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 properties, whether 

 soft, hard, compact, porous, light, heavy, etc. ; secondly, 

 as to its chemical composition and the amount of plant 

 food contained in it. The first can be regulated by tillage 

 and drainage, the second by a proper use of fertilizers. 



Under mechanical structure is included also the power 

 of absorbing and retaining water. A good absorbent soil, 

 i.e. sand, or gravel, is not apt to be a good retainer, while, 

 clay and marl, that absorb slowly, retain well. 



347. Experiment. — Take a few handfuls of each of the 

 different kinds of soil in your neighborhood, free them as 

 thoroughly as possible from all traces of vegetation, place 

 separately in small earthen pots or saucers and keep them 

 well moistened. Pull up the seedling plants that appear 

 in each, and keep a list of them as long as any continue to 

 come up. What inference would you draw from the num- 

 ber produced in each pot as to the productiveness of the 

 different soils .■' Could all the seedlings have lived if they 

 had been left to grow where they came up ? What be- 

 comes of the majority of seedlings that germinate in a state 

 of nature ? 



PRACTICAL QUESTIONS 



1. Is the relation between man and the plants cultivated by him a 

 symbiosis ? 



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? (342.) 



3. Which of the five ecological factors described in Sections 341-346 

 has probably influenced their distribution? (342.) 



4. What is the prevailing character of the soil in your neighborhood ? 



5. Is your climate moist or dry? Warm or cold? 



6. Can you trace any connection between these factors and the pre- 

 vailing types of vegetation? 



