REGIONS OF GROWTH 213 
are, however, some plants, like the Lilac shown in Figure 194, 
in which the terminal bud is replaced by two lateral ones, 
but such is not the rule among plants. 
Growth of Stems 
Phases of Growth. — In growth three 
things occur: (1) the addition of new 
cells by the meristematic tissues; (2) the 
elongation of cells; and (3) their modifi- 
cation into tissues. The first phase must 
precede the other two, but elongation 
and modification accompany each other, 
for cells begin to modify into tissues be- 
fore completing their elongation. In 
short-lived plants, such as annuals, the 
first phase is most prominent in the seed- 
ling stage, during which most of the cells 
upon which growth in length depends are 
formed from the apical meristems. In 
Corn most of the cells are formed during 
the first three or four weeks of growth. 
During the remainder of the growth pe- 
riod the cells elongate and modify into 
the tissues of the mature stem. In per- Fie. 194.— Branch of 
ennials the three phases are repeated the Lilac, showing the ter- 
each year as is well illustrated by the minal buds replaced by two 
.__ lateral ones. 
yearly growth of trees. But even in 
trees most of the cells which have to do with the growth in 
length are formed in the buds during the previous year; and to 
their remarkably rapid elongation is due the conspicuous phase 
of spring growth in which the shoot elongates and leaves and 
flowers expand into almost full size in a few days. 
Regions of Growth. — The principal regions of growth are at 
the apices of stems, where growth in length occurs by the addi- 
tion of new nodes and internodes, and at the cambium layer, 
where growth in diameter takes place. In such stems as those of 
the Grasses, the basal portion of each internode functions for some 
time as a meristem and thereby aids in the growth in length of the 
internode. It is due to this feature that Corn stems, before they 
