94 THE OAK 
forming an almost continuous ring (fig. 24, se.ph), and 
consisting chiefly of the sieve-tubes and cells developed 
from the cambium cylinder, the small primary phloém 
Vic. 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 phloém, 
pr.ph, and outside the primary xylem, p7.2; and the 
larger figure shows the results of its activity in the 
formation of secondary phloém, se.yh, inside the primary, 
and secondary xylem, s¢.v, between the primary xylem 
eroups. In both cases, ep, piliferous layer; ¢, cortex; 
P, pith; sh, endodermis. Within the latter lies the 
pericycle, in which the cork cambium, c.cam, is now 
developed. 
