CHAPTER VIII 



STRUCTURE AND WORK OF STEMS 



56. The Primary Use of the Stem is to hold the leaves 

 up where they may be fully exposed to the light. Sun- 

 light furnishes the energy for the food-making work. 

 Of course, when the leaves are more exposed to ^. 

 the light and winds, evaporation is increased. 

 Therefore, stemmed plants need more water than 

 stemless ones. 



57. The Growing Point of the Stem 

 is in the bud at the end. The cells at 

 the growing tip are very small and 

 delicate. The young sections, or inter- 

 nodes,* grow in length, forming the 

 stem. The stem length- 

 ens by the multiplica- 

 tion and growth of the 



cells. All the cells are 

 much alike at first, but, 

 as the cells lengthen, so 

 does the stem. Many 

 changes take place. 

 Soon there are several 

 kinds of cells and ves- 

 sels, as shown in Fig. 22. 

 Some are elongated, 



Fig. 22. Cross-section of a woody stem. 

 Upper one actual size, a, pith: b, d and 

 e, water ducts; c, woody portion; /, 

 phloem; g, h, and t, outer protective 

 layers. After Goodale. 



*The use of the words nodes and intemodes is made necessary by the double 

 use ot the word "joint. ' 



(34) 



