482 



On the Structure of Boots. 



cortical and the woody or central region : the former of these is 

 altogether parenchymatous, the latter consisting for the most 



part of woody tissue in 

 ^'g- ^- /Sis^J7?K. natural roots, but con- 



taining abundance of 

 parenchyma in plants 

 where the roots become 

 fleshy. 



The cortical region 

 (fig. 8) is continuous 

 with the rind-structure 

 of the stem, and in 

 young roots consists of 

 a thin layer of squarish 

 parenchymatous cells, 

 more or less densely 

 filled with mucilaginous 

 contents, but completely 

 covered in on the outer 

 surface by a layer of 

 cells firmly connected 

 side by side, forming a 

 kind of skin, called the 

 epidermis. This skin 

 is distinguished from 



a, cross, and b perpendicular, slice of the root of a seedling that clothing the leaveS 

 carrot magnified sixty diameters. The central woody por- i 



tion contains great quantities of ducts, and a delicate "•H'^ 

 cambial layer intervenes between this and the rind. 



Fig. 9. 



young shoots, in 

 accordance with the dif- 

 ference of function, by 

 the absence of the pe- 

 culiar breathing-pores 

 or stomata, by which the 

 internal structures of 

 the leaves, &c., are 

 placed in direct com- 

 munication with the 

 atmosphere. There are 

 no openings of any kind 

 through the skin cover- 

 ing the surface of roots ; 

 and the notion formerly 

 entertained of the exist- 

 ence of sponge-like re- 

 gions at the extremities 

 of roots was an error 

 arising out of imperfect 



Magnified fragment of a fine rootlet of a turnip, showing the , " .. ^-i, 



fibrils or radical hairs on the surface. observation, aS Will ap- 



