n8 
THE VEGETATIVE FUNCTIONS OF PLANTS 
growth in length of roots is largely confined to a zone a 
few millimeters in length directly back of the root-tip. 
It should also be noted in this connection that the zone 
of root-hairs begins just back of the zone of growth, no 
root-hairs being found in the region of elongation. 
FIG. 77. Experiment to show the method of growth in length of a root. 
A , 24 hours after the condition shown in the glass. 
121. Elongation of Stems. The manner of elongation 
of stems may be ascertained by marking the internodes 1 
of a young growing stem throughout their entire length. 
Two or three adjacent internodes near the tip of the stem 
should be marked. After a period of from 24 to 36 hours 
the marks will be found to have separated, but, in con- 
trast to the behavior of the root, the marks will be found 
to have separated through the entire extent of the inter- 
node, and several adjacent internodes will be found to 
have elongated at the same time (Fig. 78). This con- 
tributes to the more rapid elongation of the stem, and is 
1 An internode is the space between two successive leaves on the stem. 
