CHAPTER Y 

 STEMS 



76. What the Stem is 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 XI). The stern is that part or organ of the plant 

 which serves to bring roots and leaves into communication 

 with each other. In most flowering plants the stem also 

 serves the important purpose of lifting the leaves up into 

 the sunlight, where alone they best can do their special 

 work. 



The student has already, in Chapter III, learned some- 

 thing of the development of the stem and the seedling ; 

 he has now to study the external appearance and internal 

 structure of the mature stem. Much in regard to this 

 structure can conveniently be learned from the examina- 

 tion of twigs and branches of our common forest trees in 

 their winter condition. 



77. The Horse-Chestnut Twig. 1 Procure a twig of horse-chest- 

 nut eighteen inches or more in length. Make a careful sketch of it, 

 trying to bring out the following points : 



(1) The general character of the bark. 



1 Where the buckeye is more readily obtained it will do very well. Hick- 

 ory twigs answer the same purpose, and the latter is a more typical form, 

 having alternate buds. The magnolia or the tulip tree will do. The student 

 should (sooner or later) examine at least one opposite- and one alternate-leaved 

 twig. 



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