THE STEM AND THE LEAF 63 
groups: one with no continuous woody cylinder, like the stem 
of such a climber as the Dutchman’s-pipe (fig. 42, 1), and one 
with « continuous wooly cylinder, like that of the sunflower 
(fig. 42, B). The real difference between the two kinds of stem 
is that, like most climbers, the stem of the Dutchman’s-pipe 
begins the season’s growth with a set of separate fibrovascular 
bundles which remain separate, while in the sunflower the 
bundles are at first sepa- 
ae ep cort b v h 
rate but soon join each other. epee TT eeariamea: “P 
aN 
The boundary between bark ian 
and wood is a layer of thin- a 
walled cells (c, fig. £2, 4), BS | 
5 A at 
the cambium layer. It is aR 
this cambium, its cells filled ey 
with mucilaginous proto- SE] 
plasm, that makes up the Be | 
slimy layer just outside BS] 
the wood, from which the Be 
0) 
000 
bark peels so readily in 
early spring, when boys are 
making whistles or strip- 
ing off sheets of slippery- 
ee a ees ep, epidermis; cort, cortex; b, bast; v, ves- 
elm bark. It is Important sels; sh, sheath surrounding pith; p, pith; 
to notice that each fibro- sé, sieve cells of the bast. Magnified about 
vascular bundle eoneiaie of 90 diameters. After Bonnier and Sablon 
an outer portion, 0, which belongs to the bark, and an inner 
portion, 7, which belongs to the wood. 
A much better idea of the details of structure of the several 
regions of the stem can be gained from a lengthwise section, 
like that shown in figure 43, than from cross sections, like 
those of figure 42.1. The uses of some of the parts shown 
in figure 43 are briefly stated on the following page. 
1 Since the type of stem structure shown in figure 43 is not exactly like 
that of the other two figures, it will not be possible to identify all the kinds 
of cells shown in figure 48 with those of the other two. Note especially that 
in figure 48 the cambium is not readily distinguished from the overlying 
tissues, and that no distinct layer of heavy-walled bast fibers is found. 
C0 
Fic. 43. Lengthwise section of a young 
dicotyledonous stem 
