The Stem. 81 



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

 whence roots usually start first in cuttings and layers 

 (358, 349). 



116. The Stem Lengthens by Elongation of the 

 Internodes, as well as by the formation of new ones. 

 As the internodes soon attain their ultimate 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 per- 

 ennial plants that are only partly elongated at 

 the close of the growing season in general re- 

 main undeveloped. When growth is resumed 

 in spring, the formation of a comparatively long 

 internode beyond the very short ones of au- 

 tumn usually forms a perceptible ring about 

 the shoot, which enables us to readily locate the 

 \a point at which growth started in the spring 

 (Fig. 36). Indeed we caii often determine the 

 amount of growth that took place during the 

 preceding season or even farther back. 

 uS> G n 3 6 f II7 ' The Ultimate Length of the Inter- 

 oidlr and n des i n an y plant, or any part of a plant, 

 wood. 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 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 

 young internodes that are not unduly shaded is gener- 

 ally in proportion to their length, hence rapid'y-grow- 



