222 



STRUCTURE AND VITAL PROCESSES OF PLANTS 



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2. THE ROOT 

 A. The Work done by the Root and its Main Types. 



1. A plant derives its raw food partly from the air (Carbon 

 dioxide) and partly from the soil (water and mineral salts). 

 Hence one part of its body, the shoot, rises above the ground 

 into the air, whereas its other part, the root, grows downward 

 into the soil to absorb water and mineral salts- 



But in order that the over-ground parts of a plant may not 

 be thrown over by the wind, the plant must be tirmly anchored 

 in the soil. And this is another function of the root. 



2. As we can 

 see in the germi- 

 nating seed of a 

 horse gram (p. 31) 



th e r ot th a t form s i;^si^^^^^^K xf ^^ 

 the continuation 

 of the hypocotyl, 

 the main or tap- 

 root, works its 

 way vertically 

 into the soil. 

 Branching from 

 it there issue 5/f/e- 

 roots in all direc- 

 tions, more or 



less slanting or even horizontally. 



It may be noticed, e. g., in the 



swollen root of the Carrot, that such 



side-roots are arranged in vertical 



rows, and that the epidermis of the 



main root is rent where the side- 

 roots issue. As the side-roots grow 



and divide into finer and tiner roots, the whole soil within the 



reach of the plant is traversed by liundreds and thousands of 



rootlets. 



Fig. 202.— Main root 



with side-roots of 



Thorn-apple. 



\ 



Fig. 203.- Carrot. Tap-root of 

 Carrot with small side-roots. 



