CHAPTER XV 

 STEMS AND BRANCHES AND THEIR USES 



206. Growth of the Stems of Seed Plants. We have seen 

 that, while new cells are being formed in the embryonic re- 

 gion at the tip of a stem, the older cells just back of the tip 

 are growing longer. We have seen too that at the tip of the 

 stem appear small swellings which are to grow into leaves 

 and branches. The place on the stem at which a leaf (or a 

 pair or circle of leaves) is attached is called a node; the part 

 of the stem between two successive nodes is an internode. 

 The swellings that will become leaves are at first very close 

 together. The growth of the cells back of the tip pushes 

 the young leaves somewhat farther apart and so lengthens the 

 internodes. Some stems have little or no growth in length 

 excepting this near the tip. Such a stem grows slowly and 

 its internodes remain comparatively short. The stems of 

 many palms grow in this way ; but some of them live long 

 enough and form enough short internodes so that they be- 

 come tall trees. But in the stems of most seed plants growth 

 continues for a time also in the older parts that is, in the 

 parts below the terminal bud . This growth is usually in the 

 internodes, so that for some time the young leaves are pushed 

 farther and farther apart. Growth of this kind is seen in the 

 cucumber, the bean, the corn, and indeed in most of our 

 common plants. 



The length to which the internodes grow varies greatly in 



different plants ; it is much affected, too, by the nature of 



the soil and by conditions of light, heat, and moisture. This 



is why, of two plants of the same variety grown under differ- 



186 ' 



