THE SEEDLING AND YOUNG PLANT 



27 



If, in addition to these successive transverse sections, 

 we examine a carefully prepared longitudinal section, 

 cut so as to pass accurately 

 through the median plane of 

 the root, the comparison not 

 only establishes the above con- 

 clusion, but it enables us to be 

 certain of yet other facts (fig. 6). 

 Such a section shows the root- 

 cap covering the tip as a thimble 

 the end of the finger, and the 

 rim of this root-cap is evidently 

 fraying away behind ; the cells 

 of which it is composed die 

 and slough off as the root 

 pushes its way between the 

 abrading particles of soil. Ob- 

 viously this loss of worn-out 

 tissue must be made good in 

 some way, and closer exami- 

 nation shows how this occurs. 



r.c. 



The extreme tip of the root FIG. 6 Diagrammatic sec- 

 proper fits closely into the cap, 

 and evidently adds cells to the 

 inside of the latter, and thus 

 replaces the old ones which are 

 worn away. At this true tip 



of the root, moreover, we make another discovery 

 namely, that all the cells are there alike in shape, size, 



tion through the end of the 

 root of the oak. c, root- 

 cortex ; e, piliferous layer ; 

 re, root- cap ; m, the true 

 embryonic tissue (so- 

 called ' growing-point ' ) ; 

 ph, phloem ; a*, xylem. 



