Chapter Five 

 ROOTS 



The root will be used as a beginning point for a detailed 

 study of the structure of the various parts of the plant. 

 This will be followed in the two succeeding chapters by root 

 functions as related to the soil. Roots are usually the least 

 studied of any part of the plant because they are inconspicu- 

 ous and difficult to free from the soil. When their important 

 functions are appreciated it becomes clear that they are of 

 the utmost importance for the best growth of the plant. 



The root systems of plants are divided into primary, 

 secondary, and adventitious roots. The primary root of a 

 plant develops directly from the seed when it germinates. 

 The roots coming from the primary root and all their 

 branches are known as secondary roots (Figs. 4 and 5) . All 

 other roots, whether they arise from stems or leaves, are ad- 

 ventitious roots. All secondary roots originate within the 

 root while it is young, near the xylem region, and push 

 through the outer tissues into the soil. 



Root systems are divided into two groups according to 

 the nature of their growth. A tap root system results from 

 the continuous and vigorous growth of the primary root, 

 such as in carrots, alfalfa, and many of the trees. The gar- 

 den carrot has a tap root, the top of which is modified for 

 food storage but a thin part of it may penetrate the soil more 

 than seven feet, according to Weaver and Bruner in their 

 book on "Root Development of Vegetable Crops." They 

 found the secondary roots extending in every direction from 

 the tap root to a distance of two and a half feet or more. 



A longitudinal view of a carrot may be used to describe 

 some of the structures common to young roots. The central 



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