106 



MINUTE STRUCTURE OF THE ROOT. 



THE ROOT. 

 PRIMARY STRUCTURE. 



OIllj 



differences exist between these 

 cells, both as regards shape 

 and size ; at the very end of the 

 radicle the}- are relatively large, 

 and form a sort of cap-like cov- 

 ering (root-cap] for the smaller 

 cells lying directly back (the 

 growing-point). If the section 

 is thin enough, it will be seen 

 that at the growing-point numer- 

 ous rows of cells appear to con- 

 verge, the fact being that all the 

 cells of such rows are derived by 

 multiplication from those at the 

 growing-point. 



321. Certain differences in the 

 arrangement of these rows can 

 be seen upon comparing the radi- 

 cles of plants of different classes. 



319. It was stated in Vol. 

 I., p. 27, that the root, or 

 descending axis, " normally 

 begins in germination at the 

 root-end of the caulicle, or 

 so-called radicle ; but that 

 roots soon proceed, or may 

 proceed, from other parts of 

 the stem, when this is favor- 

 ably situated for their pro- 

 duction." 



320. A longitudinal sec- 

 tion through the tip of a 

 germinating radicle exhibits 



parenchyma cells. Slight 



FIG. 85. Longitudinal section through the middle of the root-tip of Fagopyrnm escu- 

 lentum. The lower initial cells prive rise to the cap c, ami the epidermis e'p ; the middle 

 produce the cortex c'e ; ;><?, peripheral layer of the central cylinder cc, which comes 

 from the upper initial cell*. (Janczewskl.) 



Fio. 86. Longitudinal section through the middle of a lateral root of Pontederla 

 crassipes: cc, nascent central cylinder (plerom); r'c, nascent cortex (periblem); e'p, 

 nascent epidermis (dermatogen) ; c, root-cap. (Flahaulfc.) 



