76 PLANT LIFE 
cell becomes directly continuous with those 
of longitudinally adjacent cells. Such tubes, 
which have arisen by the disappearance of 
—— 
a gS 
‘i 
7 
Fig. 11.—Diagrammatic section of young wood stem. B, B, 
bast; C, C, cambium; E, epidermis; M, later wood; P, 
the first wood formed (protoxylem); Pi, pith; R, rind; 
S, stoma; V, V, vessel; WP, wood parenchyma. 
walls, are often called vessels. The water- 
conducting cells which keep their walls intact 
are termed tracheids. The tracheids and 
vessels then form the special tissues in the 
