58 



STRUCTURE OF THE ROOT 



a mantle of cells, the root cap. This cap protects the delicate 

 cells within like a thimble so that they are not exposed or injured 

 as the root extends through the soil. At the tip of the root, just 

 within the root cap, the cells are actively dividing and adding 

 new cells to the end of the root and some cells are also added 



Fig. 32. Later stages in the division of the cell: E, the fibrillae pulling 

 the separated halves of the chromosomes to the opposite poles of the spindle. 

 The inner series of fibrillae are now seen at the equator between the two 

 groups of chromosomes. F, the chromosomes arranged at the poles and the 

 inner fibrillae increasing in size and number. G, the fibrillae have increased 

 in number until they nearly reach the opposite walls of the mother cell. Their 

 thickening at the equator is the first indication of the wall separating the two 

 new cells. H, position of the new wall clearly indicated. — I. D. Cardiff. 



to the inner side of the root cap (Fig. 34). Owing to this unique 

 arrangement it does not matter if the outer cells of the cap are 

 injured or destroyed as the root pushes through the soil, because 

 the cap is constantly being renewed from within, and so always 

 furnishes adequate protection to the delicate cells within. The 

 cells that are added to the tip of the root divide several times 

 after their formation, so we find that the tip of the root for a 

 distance of one, or two mm. is composed of small cells that are 

 in a process of division but that are enlarging to only a slight 

 degree (Fig. 34). This region is called for this reason the for- 

 mative region of the root. Back of the formative region for a 

 distance of two or four mm. the cells are dividing to a less degree 

 but are elongating very rapidly and changing in form (Fig. 35). 

 This is the region of rapid elongation. Still further back elonga- 

 tion has ceased, but the walls of the cells are becoming thicker 



