CHAPTER XL 



CLASSES OF PLANTS AND THEIR ECONOMIC IMPORTANCE 



Questions. 1. What is a weed? Why are there weeds? 2. Is every 

 plant that grows either useful or harmful to man? 3. What is the most 

 useful family of plants ? 4. Do all the useful plants belong to the same 

 family ? 5. Are there any families of plants that are altogether good or 

 altogether bad for man ? 6. Are there any plants of which we can use 

 all parts ? 7. Do all trees belong to the same family ? 8. What makes 

 some woods more valuable than others ? 



316. Meaning of economic relations. The word economic 

 comes from a Greek word meaning '^ house," and formerly per- 

 tained to the management side of housekeeping. It has gradu- 

 ally come to mean "pertaining to wealth and welfare" in so far 

 as well-being depends upon material things. In this sense we 

 speak nowadays of the economic importance of anything when 

 we have in mind its contribution to or interference with human 

 welfare. All the utilities that we can find in a plant, as well as 

 all the injuries that it may cause, either directly or indirectly, 

 make up its economic relations. Most important groups of 

 plants and animals have members that are of some use to us, as 

 well as members that are in some way harmful. Indeed, a single 

 species may be both a source of satisfaction and a source of 

 trouble. The dog, for example, has long been man's friend and 

 is of value in many ways ; but he is also a potential means of 

 bringing the dreadful disease rabies, and more than once a dog, 

 like Carlyle's "Diamond," has been the cause of serious loss to 

 his master. 



A large part of man's practical activity is organized on a com- 

 mercial basis— that is, on the basis of buying and selling, or 

 exchanging goods and services, with money passing between 



buyer and seller. Still, there are many values in life which 



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