214 
GROWTH OF STEMS 
reach maturity, are easily broken off just above the node. Fur- 
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Fic. 195. — Lengthwise 
section through the stem 
thermore, in having this meristematic 
zone, stems of the Grasses, when blown 
down, are able to become partially erect 
by bending in the region of the node due 
to a more rapid growth of this region on 
its lower side. 
Since the stem segments are added 
in succession at the apex, a stem soon 
comes to have segments in various stages 
of development, for while those at the 
apex are just beginning to elongate, those 
at the stem’s base may have completed 
their elongation and formation of tissues. 
This feature is illustrated in Figure 195, 
although none of the segments are yet 
mature. 
Primary and Secondary Growth. — In 
both stems and roots, apical growth, 
since from it the tissues of the stem and 
root first originate, is called primary 
growth, while growth from the cambium 
is known as secondary growth because it 
is chiefly concerned with adding more 
tissues of the same kind to those already 
formed from the apical meristems. Tis- 
sues are also called primary or secondary 
according to whether they originated 
from the primary meristems or from the 
cambium. 
Character and Rate of Growth in 
Stems. — Since elongation or enlarge- 
ment is the most conspicuous phase of 
growth, it is employed in determining 
the character and rate of growth. Al- 
though the most conspicuous, neverthe- 
of a Corn plant, the plant being about two feet high. 1, leaves; ¢, tassel; 
7, region of stem where internodes have not elongated, a, internodes which 
have undergone the most elongation; 6, meristematic region at the base of 
the internodes. 
