THE ROOTS OF PLANTS. 



103 



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, a 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 : 

 Ji. the same advanced somewhat, the inner layer is beginning to divide; C, young 

 root enclosed in the tissue of the mother-root ; Ji. r, cortex ormother-root ; IT, 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 6 ; i, n, mass 

 of cell- resulting from the division of the layer n in A ; 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 

 Reiiike. 



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. 



