156 APPLIED BIOLOGY 



information regarding many points concerning the physiology or 

 activities of germinating seeds. 



ROOTS OF SEED-PLANTS 



146. Structure and Kinds of Roots. The structure of 

 all roots of seed-plants is essentially like that described for the 

 bean plant; namely, bark or rind with its outermost layer of 

 epidermis, a central woody axis with tubes for conducting 

 water upward, and the epidermal root-hairs near the ends of 

 the young rootlets. See 67. 



As to the kinds of roots, some plants have a main root 

 which grows downward and gives off smaller roots laterally. 

 This is a tap-root; carrot and radish are good examples. 

 In many plants no such main root can be distinguished. 

 Examples are the much-branched roots of Indian corn and 

 many grasses; and such roots are called fibrous. Tap- 

 roots when thickened by food-storage are said to be fleshy 

 (e.g., carrot). It should be noted that a carrot or radish 

 as seen in markets is not all root, for the upper end is thick- 

 ened stem with a bud for next season's growth. 



(L) Pull up as many different kinds of cultivated plants and 

 weeds as possible, examine the roots, and make sketches of the 

 different forms of roots seen. 



147. Roots as Anchors and as Absorbers. The two 

 primary functions of roots, anchoring plants in soil and ab- 

 sorbing water with useful substances in solution, are carried 

 on in all roots essentially as described in the preceding chapter 

 on the work of the bean plant (see 86). 



148. Roots Fitted for Growth in the Soil. The root-cap, 

 already studied ( 68), protects the growing tip from injury 

 as the root pushes between the particles of the soil. The 

 fact that increase in length takes place near the growing 

 tip (Fig. 34) may be of advantage in curving to pass around 

 stones and other obstructions, and in turning towards 

 moisture and food. The primary root grows downward. 



