THE ROOT 



101 



dead cells but are sound and give support to the trees. Some- 

 times the heart- wood decays and the tree becomes hollow but 

 continues to live and grow so long as the cambium is uninjured. 

 The root (Figs. 75 and 76) is composed of the same tissues 

 as the stem, but they are arranged in an entirely different man- 

 ner. In the centre is the central cylinder or axis made up of 

 fibro-vascular bundles which are separated by thin layers of 

 parenchyma. Immediately surrounding this axis is a compar- 

 atively thick zone of parenchyma cells known as the cortex. This 



FIG. 75 



FIQ. 76 



FIG. 75. Diagrammatic longitudinal section of root tip showing: a, axis cylinder; c, cortex; 



e, epidermis; x, root cap. 

 FIQ. 76. Cross-section of root tip showing cellular structure and root-hairs. 



is surrounded by a very thin layer of cells known as the epi- 

 dermis. The epidermis of the very young roots gives rise to a 

 great number of extremely delicate root hairs which penetrate 

 the soil and take the water and necessary substances which may 

 be in solution. (Page 26.) 



