THE ROOT 



63 



the office of the stem, until there is practically no difference 

 between them. On the sides of gullies, where the earth 

 has been washed from around the trees, we often see the 

 upper portion of the root covered with a thick bark and ful- 

 filling every office of a true stem. 



67. Minute structure of the root. (a) Mount in water 

 and place under the microscope a portion of the root of an 

 oat or radish seedling containing a number of hairs. In 

 studying the thin, transparent roots of very young seedlings 

 a section will not be necessary. Observe whether the hairs 

 originate from the epidermis or 

 from the interior. Are they true 

 roots, or mere outgrowths from h' 

 the cells of the epidermis? Do 

 they consist of a single cell or a 

 number of cells each? Notice 

 what very thin cell walls the 

 hairs have ; is there any advan- 

 tage in this ? The interior, trans- 

 parent portion of the hair con- 

 tains the sap, and the protoplasm 

 forms a thin lining on the inner FlG 79 _ Longitudinal section 



Surface of the Wall; why not through the tip of a young root, some- 

 .. , , what diagrammatic : h, h, root hairs ; 



the Sap next the Wall and tile epj epidermis; a, cortex; b, central 



cylinder; e, sheath of the cylinder 

 (endodermis) ; g, growing point ; c, 

 root cap ; d, dead and dying cells loos- 



ened from the extremity of the cap. 



protoplasm in the interior ? (58, 

 60.) 



(b) Next examine a portion 

 of the body of the root and try to make out the parts as 

 shown in Fig. 79, and compare them with your observa- 

 tions in 64. The light line running through the middle is 

 the central cylinder, up which the water passes, as was shown 

 by the colored liquid in 64. Outside this is a darker por- 

 tion (a, Fig. 79), corresponding to the cortex (rr, Fig. 77). 

 Besides other uses, the cortex serves to prevent the loss 

 of water as it passes up to the stem, and also, in fleshy 

 roots like the carrot and turnip, for the storage of nourish- 



