TEE BOOT AND THE SOIL 73 



a whole, the part between the nodes, is called an in- 

 ternode. 



The nodes are distinctly marked in the younger stems 

 of most plants by a slight enlargement or by leaf-scars, 

 if the leaves have fallen (Fig. 35). The nodes are centers 

 of vital activity and are points at which lateral growing 

 points (buds, 127) are normally formed, and whence 

 roots usually start first in cuttings and layers (358, 349). 



116. Lengthening of stem. — The stem 

 lengthens by elongation of the internodes, 

 as well as by the formation of new ones. 

 As the internodes soon attain their ulti- 

 mate length, it follows that the stem 

 lengthens only near its distal end. An 

 internode that has once ceased elongating 

 does not usually resume it, hence the 

 internodes of perennial plants that are 

 only partly elongated at the close of the 

 growing season in general remain unde- 

 veloped. When growth is resumed in 

 spring, the formation of a comparatively 

 long internode beyond the very short ones 

 of autumn usually forms a perceptible Fig- 36. — Union 

 ring about the shoot, which enables us older°wood^° 

 to readily locate the point at which growth 



started in the spring (Fig. 36). Indeed we can often de- 

 termine the amount of growth that took place during the 

 preceding season or even farther back. 



117. Length of internodes. — 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 

 internodes, and vice versa. In the same species, therefore, 

 the average length of the internodes is much greater in 



