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 

 ^ greatly thickened and somewhat modified epidermis. 



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

 ^, a portionof the pericamblum tt, bounded exrernaily by the innermost layer of cor- 

 tical ceUa, r; d, dermatogen ; n, the inner layer of the pericamhium after splitting ; 

 JS, the same advanced somewhat, the inner layer ia beginning to divide; C, young 

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

 cambium of mother-root, from which the new root has been formed ; h, first layer of 

 the root-cap of the new root, formed by the splitting of its dermatogen h ; i, w, mass 

 of cell!^ resulting from the division of the layer n\nA; D, new root further devel- 

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

 conical tissue of mother-root) ; p, p, periblem of new root ; m, m, the tissue which 

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

 Beinke. 



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. 



