EL( INGATK »X < IF THE R< >< » I" 



thickening goes on assisted by the addition of now fibrillar at 

 either si«K- of the spindle until a delicate line < the cell wall > reaches 

 - the old cell I Fig. 32, //>. 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, it 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 1 Fig. 33) we see that the tip of the root is covered with 

 a mantle of (.•ells, 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 to the inner side of the root 

 cap i Fig. 34). ( >wing 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 constantl) being renew eel 

 lg from within, and so always furnishes adequate pro- 

 tect ion 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 



'" "'■ 33' root for a distance of one or two mm. is com] 

 ram of a . . . ...... 



n| small cells that are in a process 01 division hut 



that arc enlarging to only a slighl degree 1 Fig. 34 I. 

 This region is called for this reason the formative 

 region of the root. Back of the formative region for 



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



to a less degree hut are elongating ver) rapidly and 

 changing in form 1 Fig. 35). This is the region of 

 rapid elongation. Still further back elongation has ceased, hut 

 the walls of the cells are becoming thicker and the cells are chang- 

 ing in character, so that the) perform different duties. This is 

 illustrated in the CTOSS section of the foot i Fig. 36), where w< 



that the outer cells have become modified, forming an epidermis 



on taken 

 through the 

 center of 1 

 corn r< >« >t : r, 

 rool cap; t 

 epidermi 



. cen- 

 tral region. 



