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 conclusion, but it en- 

 ables 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 be- 

 hind ; the cells of which it is 

 composed die and slough off as 

 the root pushes its way between 

 the abrading particles of soil. 

 Obviously this loss of worn-out 

 tissue must be made good in 

 some way, and closer examination 



shows how this occurs. The ex- 



\i*.c. 

 treme tip of the root proper fits ,-, 



FIG. 6. Diagrammatic sec- 



closely into the cap, and evident- tion through the end of 

 ly 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, more- 

 over, we make another discovery, 

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

 size, and other peculiarities ; and if we could take a 



the root of the oak. c, 



root-cortex ; e, piliferous 

 layer ; re, root-cap ; ra, 

 the true embryonic tis- 

 sue (so-called " growinsf- 

 point ") ; ph, phloem ; x, 

 xylem. 



