Then, inside this periderm we shall find the phloëm forming an almost continuous ring (Fig. 24, se.ph), and
_Fig_24.jpg)
Fig. 24.—Transverse sections (semi-diagrammatic) of roots of oak, to be compared with Fig. 7. The smaller figure, above, shows the cambium ring, cam, now developed as a continuous layer running inside the primary phloëm, pr.ph, and outside the primary xylem, pr.x; and the larger figure shows the results of its activity in the formation of secondary phloëm, se.ph, inside the primary, and secondary xylem, se.x, between the primary xylem groups. In both cases, ep., piliferous layer; c, cortex; P, pith; sh, endodermis. Within the latter lies the pericycle, in which the cork cambium, c.cam, is now developed.
consisting chiefly of the sieve-tubes and cells developed from the cambium cylinder, the small primary phloëm
