CHAPTER VIII 



ROOTS 



General Features of Roots 



The higher plants consist of roots and shoots. The roots are 

 generally underground structures, while the shoot is the aerial 

 portion consisting of the stem with its leaves, buds, flowers, and 

 fruit. Plants like the Algae, which live in the water where all parts 

 of the plant can absorb directly from the surroundings, do not 

 need roots, although they often have structures known as hold- 

 fasts which anchor them ; but holdfasts are too simple in struc- 

 ture to be called roots. Even in the Mosses, which are mainly 

 land plants, instead of roots there are hair-like structures, called 

 rhizoids, which anchor the plant to the substratum. True roots 

 are complex structures and are characteristic of Ferns and Seed 

 Plants. 



Although we think of roots as underground structures, there 

 are, however, a few plants having roots adapted to living in other 

 situations, as in the water, air, or the tissues of other plants. 

 But with few exceptions our cultivated plants depend upon soil 

 roots, which, therefore, deserve most attention. 



Being underground structures, soil roots normally arise from 

 the stem's base, from which they radiate by elongating and grow- 

 ing new branches, which in turn branch and rebranch until the 

 soil about the plant is quite thoroughly invaded by its root sys- 

 tem. Usually a plant's root system, tapering into numerous 

 branches almost hair-like in size, is more branched and spreads 

 farther horizontally than its stem system. The profuseness 

 with which roots branch is well shown by the estimated root 

 length of some plants. Thus the length of all the roots of a single 

 Wheat or Oat plant, laid end to end, is estimated at 1600 feet, or 

 more than a quarter of a mile. For a vigorous Corn plant the 

 estimated root length is more than a mile. Certainly in some 

 trees the root length would much exceed that of Corn. 



The size of a plant's root system, in general, varies with that of 



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