ii8 



THE VEGETATIVE PUNCTIONS 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' 

 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 



' An internode is the space between two successive leaves on the stem. 



