MORPHOLOGY OF THE BOOT. 29 



simple microscope of a slender j'oung root, and of thin slices 

 of it immersed in water, may serve to give a general though 

 crude idea of the vegetable cellular structure, sufficient for the 

 present purpose. Roots are naked ; that is, they bear no other 

 organs. When they send off branches, these originate from the 

 main root just as roots originate from the stem ; and in both 

 cases without much predetermined order. The ultimate and 

 veiy slender branches are sometimes called root-fibrils ; but 

 these are only delicate ramifications of the root. Like any 

 other part of the plant, however, roots may produce hairs or 

 such like growths from the surface, which are wholly distinct 

 from branches. (383.) ~7> * of 



46. Root-hairs. Roots absorb water, &c., from the soil by 

 imbibition through the surface ; that is, through the walls of the 

 cells, which are in a certain sense permeable to fluids, more readily 

 when young and tender, less so when older and firmer. Roots, 

 therefore, absorb most by their fresh tips and adjacent parts ; 

 and these are continuall}- renewed in growth and extended fur- 

 ther into the soil. As the active surface of a plant above ground 

 is enormously increased by the spread of foliage, so in a less 

 degree is the absorbing surface of }'oung roots increased b}- the 

 production of root-hairs. (Fig. 64, upper part, and more magni- 

 fied in Fig. 65, 66.) These are attenuated outgrowths of some 

 part of the superficial cells into capillary tubes (only one from 

 each cell) , closed at the tip, but the calibre at base continuous 

 with the cavity of the cell ; into which, therefore, whatever is 

 imbibed through the thin wall may freely pass. These appear 

 (as Fig. 64 shows) at a certain distance behind the root-tip. 

 Further back the older or effete root-hairs die away as the cells 

 which bear them thicken into a firmer epidermis. 



47. To the general statement that roots give birth to no other 

 organs, there is this abnormal, but by no means unusual excep- 

 tion, that of producing buds, and therefore of sending up leafy 

 branches. Although not naturally furnished with buds in the 

 manner of the stem, yet many roots have the power of originat- 

 ing them under certain circumstances, and some produce them 

 habitually. Thus Apple-trees and Poplars send up shoots from 

 the ground, especially when the superficial roots arc wounded. 

 And the roots of Maclura or Osage Orange so readily originate 

 buds that the tree is commonly propagated by root-cuttings. 



48. Kinds of Roots. The root, commonl}- single, which origi- 

 nates from the embryo itself, is called the PRIMARY ROOT. (37.) 

 Roots which originate from other and later parts of the stem, 

 or elsewhere, are distinguished as SECONDARY ROOTS. But the 



