THE BOOTS OF PLANTS. 



163 



of the root-cap originate by the successive divisions of the 

 dermatogen cells by partitions parallel to the curved surface 

 of the root-tip. As the dermatogen is continuous with the 

 epidermis, we may regard the root-cap as morphologically 

 a greatly thickened and somewhat modified epidermis. 



Fig. 139.— Mode of formation of the lateral roots in a mother-root of Trapa natans. 

 A EL portionof the pericambium tt, bounded externally by the innermost layer of cor- 

 tical cells, r; d, dermatogen ; n, the inner layer of the pericambium after splitting ; 

 B the same advanced somewhat, the inner layer is beginning to divide; C, yonng 

 root enclosed in the tissue of the mother-root ; S. r, cortex of mother-root ; tt, pen- 

 cambinm of mother-root, from which tiie new root has been formed ; k, first layer of 

 the root-cap of the new root, formed by the splitting of its dermatogen b ; i, «., mass 

 of celN resulting from the division of the layer nm A ; D, new root further devel- 

 oped (the thick cortical tissues of the mother-root are not shown ; r, inner layer of 

 corticai tissue of motlier-root) ; p^p, periblem of new root ; m, m, the tissue wiiich 

 connects the new root with the tissues of the mother-root. Magnified.— After 

 Eeinke. 



The plerome column is a mass of nascent fibro-vascular 

 elements, and in it, somewhat further back from the root-tip, 

 a differentiation into the bundle takes place. 



