68 NATURE OF THE CAMBIUM 



phloem. Each of these cells divides into two daughter cells 

 (Fig. 43), usually the inner cell (i. e., the cell next to the xylem) 



FIG. 43. Diagram showing the mode of division of the cambium cells. 

 The cambium cell is shaded to distinguish it from the cells derived from 

 it. Note in the last division at the right that the inner daughter cell be- 

 comes the cambium cell while the outer develops into a phloem cell. 



develops into a duct, tracheid, or other element of the xylem, 

 while the outer cell, after increasing to the original size of the 

 cambium cells, divides into two cells as at first. This process 

 is repeated again and again, usually the inner cell growing into 

 one of the cells of the xylem while the outer cell retains the 

 power of further division. Less commonly the reverse method 

 of growth takes place and we have the outer cell enlarging and 

 forming one of the cells of the phloem while the inner cell acts 

 as a cambium cell. In this way new cells are added to the xylem 

 and phloem and the enlargement of the vascular bundle is 

 effected. 



34. The Conducting System of the Plant. These vascular 

 bundles extend from the root up through the stem and branches 

 to the leaf where they divide again and again, reaching all parts 

 of it. In this way the bundles become much reduced in size, 

 the free end of. the vein often consisting of a single tracheid to 

 conduct the crude materials to the surrounding cells and elon- 

 gated parenchyma cells to collect the manufactured foods (Fig. 

 5, /). We now see how admirably the vascular bundles are 

 adapted to the transport of fluids. The xylem carries the sub- 

 stances received from the root hairs to all parts of the plant 

 body quickly and with a minimum expenditure of energy because 

 of the elongated character of its cells and the absorption of many 

 of the cross walls of its cells. So the manufactured foods 

 located at any point in stem or leaf are gathered up and dis- 

 tributed by the phloem, the more soluble and diffusible substances 



