51 
1920-21.] Interruption of Endodermis. 
process of cambial increase similar in its nature to that seen in the stem ; 
accordingly it was selected as an object likely to throw light on the method 
of breaking down the barrier in an enlarging part. 
The following observations were made on transverse hand sections cut 
from two roots of a plant of Draccena fruticosa grown in Glasgow Botanic 
Gardens. 
The first root examined was about 5 inches in length, and the first 
section was cut at a distance of 1| inches from the apex, and section- 
cutting was continued upwards towards the junction of root and stem. 
The first sections showed the root to be about \ inch in its greatest 
diameter, and the endodermis was a complete, almost regular ring, with all 
the cells typically thickened on the inner tangential and the two radial 
walls, the primary stele being undisturbed (fig. 1). The upward sequence 
of sections from the apex showed a gradual beginning of growth and 
division of the cells of the pericycle within the endodermis to form a 
cambium (fig. 2), and, with the slight increase in girth of the root thus 
brought about, the endodermal cells became somewhat distorted in shape, 
and the ring itself irregular ; then, finally, the sequence of endodermal cells 
was interrupted (figs. 3, 4, 5). The development of this inner or internal 
cambium began first at one part only of the sections, and was most active 
in the middle of this area, where the cambial cells divided quickly, and 
often showed four to six radial rows of cells. Above this area of active 
