106 



MINUTE STEUCTDEE OF THE EOOT. 



THE EOOT. 



Primaky Structure. 



diiferences exist between these 

 cells, both as regards shape 

 and size ; at the verj- end of the 

 radicle the}- are i-elativelj largo, 

 and form a sort of cap-like cov- 

 ering {root-cap) for the smaller 

 cells l3ing directly back (the 

 growing -poini). If the section 

 is thin enough, it will be seen 

 that at the growing-point nnmer- 

 ous rows of cells appear to con- 

 verge, the fact being that all the 

 cells of snch rows are derived I)}- 

 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, " normall}' 

 begins in germination at the 

 root-end of the caulicle, or 

 so-called radicle ; but that 

 roots soon proceed, or maj' 

 proceed, from other parts of 

 the stem, when this is favor- 

 ablv 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 Fagoiiyrum escu- 

 lentnm. Tlie lower iiiiti:il cells frive rise to the cap c, and the epidermis c'p ; the middle 

 produce the cortex e'e ,■ pc, peripheral layer of the central cylinder cc^ which comes 

 from the ujiper initial cells. (.lanczewslil. ) 



Fio. 86. Longitudinal section tlirongli the middle of a lateral root of Pontederia 

 crassipes; cc^ nascent central cylinder (plerom); e'c, nascent cortex (periblera); e'p^ 

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



