CHAPTER VI 



STEMS 



53. Nature of the stem. The work of taking in the raw 

 materials which the plant makes into its own food is done 

 mainly by the roots and the leaves. These raw materials are 

 taken from earth, from water, and from the 

 air (see Chapter xn). The stem is that part or 

 organ of the plant which serves to bring roots 

 and leaves into communication with each 

 other. In most seed plants the stem also 

 serves the important purpose of lifting the 

 leaves up into the sunlight, where they can 

 best do their special work. 



The student has already, in Chapter in, 

 learned something of the development of the 

 stem and the seedling ; he has now to study 

 the external and internal structure of the 

 mature stem. Much in regard to this struc- 

 ture can be learned most easily from the 

 examination of twigs and branches of our 

 common forest trees in their winter condition. 

 54. Position of leaf buds. The winter buds 

 of most of our trees and shrubs are formed at 



^ ^ s on tne tw jg j ust a b ove the origins of 

 r 3 J 



nal buds in Oc- the leafstalks, as shown in Fig. 79. After the 



tober fall of the leaves the buds by their positions 



b sc, Dud-scale scars, indicate where the leaves were formerly at- 



All above these , -. ,, , , . 



scars is the growth tached. They may be arranged in pairs, a bud 



of the spring and on one S {^ Q o f the stem and its mate exactly 

 summer of the ,, . . 



opposite, or they may form a spiral around 



40 



bsc 



FIG. 30. A quickly 

 grown twig of 

 cherry, with 

 lateral and termi- 



same year 



