78 Principles of Plant Culture. 
118. The Ultimate Length of the Internodes in any 
plant, or any part of a plant, depends upon the rate of 
growth,—rapid growth producing long inter- 
nodes, and vice versa. In the same species, 
therefore, the average length of the internodes 
is much greater in vigorous, young plants than 
in old ones, in the main, central shoot than in 
the branches, and when growth is well started 
in spring than during its decline in autumn. 
The diameter of the young internodes is gener- 
ally in proportion to their length, hence rapidly- 
growing shoots are usually thicker than slower- 
growing ones. We can judge of the compara- 
tive vigor of nursery trees by observing the 
Fre. 34, length and diameter of the internodes. 
Union of 
new and 119. The Stem Elongates Fastest just 
older wood. behind the growing point (67), and at least in 
young plants, just behind the primary or original growing 
point (56). When we desire to check growth of the stem, 
therefore, we remove the terminal growing point by ‘“ pinch- 
ing” (416). 
120. Pinching Stimulates Branching because remov- 
ing the terminal growing point stimulates the development 
of other growing points farther back (105). 
SEcTION 1x. THE LEAVES 
We have seen (116), that one or more leaves are normally 
formed at each node of the stem. 
12]. The Function of Leaves is Assimilation (59). 
Since assimilation takes place only in light, the cells of 
