CHAPTER VI 



THE STRUCTURE OF ROOTS 



IN the mature plant the different types of elements are grouped 

 together to form tissues subserving diverse functions. Thus, for 

 instance, one tissue, which is always superficial and has the general 

 function of protecting the underlying parts, constitutes the 

 epidermis. The vascular tissues, comprising the wood or xylem 

 and the bast or phloem, form the respective conducting systems 

 for water and mineral salts, and for elaborated food-substances, 

 whilst others largely parenchymatous in character go to form 

 the general matrix or ground tissue. It must not be supposed, 

 however, that, because there is one general function, the com- 

 ponent elements of these and other tissues are necessarily uniform 

 in character, a fact that will be best realised by the study of 

 concrete examples. 



In every young root we can distinguish a number of regions, 

 beginning with the root-cap, covering the growing point (Figs. 9 

 and 30, r.c.), and followed successively by the zone of elongation, 

 the zone bearing root-hairs, and the older part where the root- 

 hairs have withered and the lateral roots (Fig. 30, l.r.) are seen 

 emerging through the surface-layers, commonly in four or five 

 vertical rows. In a longitudinal section through the tip of the 

 root the cap is found to consist of a number of concentric layers 

 of thin-walled parenchymatous cells, whose arrangement becomes 

 less regular towards the outside (Fig. 9). The outermost cells 

 gradually become mucilaginous and break down, whilst the 

 substance of the cap is constantly renewed from the underlying 

 meristem. A little way behind the growing point (p. 20) the 

 middle of the root is occupied by a continuous, rather denser 

 strand of elongated elements, which develop into the vascular 

 tissue, and which offer a marked contrast to the thin-walled 

 parenchymatous cortex around. 

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