NATURE OF PLANTS 



53 



thickening goes on assisted by the addition of new fibrillae at 

 either side of the spindle until a delicate line (the cell wall) reaches 

 across the old cell (Fig. 32, H), and the division of the mother 

 cell into two daughter cells is completed. In this way new cells 

 are being constantly added to the root. It will be noticed, if a 

 longitudinal section through the middle of the root is examined, 

 that various regions of the elongating root may be recognized 

 owing to the difference in the character of their growth. In such 

 a section (Fig. 33) we see that the tip of the root is covered with 

 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 



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. 



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 

 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 



