62 



GENERAL BOTANY 



and elongating zones. For our convenience in describing the 

 growth of the root the tip may therefore be divided (Fig. 31, c) 

 into the following cell zones : the rootcap, the meristem (just 

 above the rootcap and inclosed by it), and the elongating, matur- 

 ing, and permanent zones. The term permanent zone, as here 

 used, signifies all that portion of the root tip in which the cells 

 have ceased to grow. In the lower portion of this zone the cells 



have not yet become 

 fully differentiated 

 into the different 

 tissues of the mature 

 root. 



Structure. Before 

 proceeding with the 

 more detailed aspects 

 of the growth of the 

 root tip it will be 

 necessary to consider 

 the cellular organi- 

 zation of the root at 

 its apex. For this 

 purpose thin sections 

 which have been es- 

 pecially prepared for 

 microscopic study are 

 necessary. First the 

 roots are embedded in 

 paraffin wax ; then the sections are cut lengthwise of the roots 

 with special section-cutting machines, or microtomes. The sec- 

 tions thus obtained are fastened on glass slides and are stained 

 by special methods for microscopic observation. In sections so 

 prepared the student can easily determine the main cell areas of 

 the growing root tip which have already been observed in living 

 roots, and can also relate the cell structure of these areas to the 

 processes of cell and organ growth. 



The cellular structure of the root tip is illustrated in Fig. 32, a 

 and 6, which are microphotographs of a portion of a root tip and 



FIG. 32. Microphotographs illustrating the cellular 

 structure of the root tip 



a, a long section through a growing root tip of 

 the false Solomon's seal (Smilacina) (the lighter 

 cells of the rootcap, the darker meristem zone, and 

 the longer cells of the elongating region are plainly 

 shown) ; b, cells of a portion of the elongating zone, 

 greatly magnified 



