STUDIES OF SEED-PLANTS 231 



surely adaptations; that is, fitted to special use ; and so, while 

 the student of biology is kept constantly on the lookout for 

 evidence of such useful structures, he must keep in mind 

 that now and then there will be found things without appar- 

 ent use. Nature has no hard and fast rule that all things 

 must be useful as seen from our human point of view. A sur- 

 prisingly large number of things are useful to the organisms 

 which possess them, but there are many puzzling exceptions. 

 220. The economic importance of the seed-plants is so 

 vast that a special book would be required to discuss it 

 adequately. Here we can only point to the fact that the great 

 majority of plants useful to man are seed-plants. Practi- 

 cally all of our plant food-supply and that of our domesticated 

 birds and mammals ; all of our forests useful for lumber ; all 

 of our plants which produce fibers (cotton, hemp, linen, etc.) ; 

 most of the plants which produce drugs and other special 

 substances ; and almost all of our ornamental plants belong 

 in the great group of seed-plants or flowering plants. The 

 mere mention of food plants, fiber plants, and lumber, calls 

 to mind the vast agricultural and manufacturing industries 

 which have been built up on the basis of seed-plants. In 

 fact, the foundation of the wealth of the civilized nations is 

 in agriculture, which is primarily the business of producing 

 useful seed-plants. With so much to the credit of the seed- 

 plants, there seems to be little remaining chance for useful- 

 ness of lower plants ; and yet we shall see that many of them 

 have special useful relations to human life. 



