GEOWTH AND CELL DIVISION 



63 



C 



of some of its cells highly magnified. Fig. 33 is a diagrammatic 

 drawing of a median long section of a root in connection with 

 which are shown camera drawings of separate groups of cells 

 taken from the rootcap, the meristem, the elongating zone, the 

 maturing zone, and 

 the permanent zone. 

 These latter drawings 

 not only indicate the 

 actual form of the cells 

 of the above regions 

 of the root but, since 

 they are all drawn to 

 the same scale, they 

 show also the increase 

 in size of the root- 

 tip cells from the 

 meristem to the per- 

 manent zone, where 

 they cease to grow in 

 length. 



The rootcap is a 

 conical mass of light- 

 colored cells that ter- 

 minates the root tip 

 and forms a protective 



mantle for the actively FIG. 33. The growth of cells in a root tip 



dividing and growing > the main areas of the root tip shaded ; b-e, camera 



. ni i r drawings of cells from the various regions of the root 



meristem Cells Which a s indicated in the figure. Note the changes in form 



lie just back of it. The and size of the cells. as growth proceeds. The nuclei 



, grow with the cells, but they occupy a proportionately 



Outer cells OI the cap smaller part of the cell cavity as the cells enlarge 



are large, thin-walled, 



and loosely joined together. Their lighter color is due to 

 the large vacuoles which nearly fill the cell cavity of each cell. 

 These outer cells are being constantly worn off as the tip of 

 the root is forced through the soil by the elongation of por- 

 tions of the root above or behind the cap cells. The inner cells 

 merge insensibly into the cells of the meristem above them and, 



