CHAPTER II 



THE ANATOMY OF THE ROOT 



THE root is one of the primary organs of the vascular plant. 

 It is typically subterranean, serving in the mechanical support 

 of the aerial portions of the axis, in the absorption and conduction 

 of water and mineral nutrients, and in the storage of reserve foods. 

 In addition to these primary functions, several additional ones may 

 be performed in specific cases, such as the development of adventi- 

 tious shoots from the fleshy root, the peculiar properties of sup- 

 port and absorption afforded by the aerial roots of certain orchids, 

 and the special nutritional functions performed by many of the 

 roots of the Leguminosae in the symbiotic relations which exist 

 between them and the nitrogen-fixing bacteria of the soil. 



Upon germination of the seed, the primary root typically grows 

 directly downward, penetrates the soil rapidly, and becomes the 

 initial absorbing and anchoring organ. Other lateral roots may 

 develop in rapid succession. In some plants, especially the 

 Gramineae, embryonic or adventitious roots from the stem are 

 present in the embryo, so that the seminal root system may con- 

 sist of a main tap root and several laterals. When the primary 

 root continues to develop and forms a conspicuous structure from 

 which numerous laterals diverge, it is referred to as a tap root 

 whether slender or fleshy. If the primary root and its laterals 

 develop more or less in equal degree and are relatively numerous, 

 the root system \s fibrous. In some cases, the primary root system 

 persists only for a relatively short time, and the permanent roots 

 arise adventitiously in a succession of whorls from the lower nodes 

 of the stem. 



Intergrades exist between the several types, and it is not uncom- 

 mon for a plant to develop a deeply penetrating tap root together 

 with a mass of fibrous surface laterals. Differences in soil texture 

 and water content, and variations in methods of cultivation often 

 affect to a very considerable degree the general configuration and 



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