CHAPTER III 



THE STEM 



31. The Function of the Stem.- — The stem has for its chief 

 function the production and display of the leaves and roots and 

 the conduction of the materials which these organs are especially 

 concerned in handling. It serves as a connection between them, 

 carrying up the material absorbed by the roots and distributing 

 the various substances received from the leaf. Like the traffic 

 of a city this material is received at many stations and trans- 

 ported along various channels to many points. At one place 

 some of it is used in the manufacture of food, at another point 

 material is required for the nourishment and construction of the 

 cells. Here a portion is stored, or again, there is the useless 

 or waste material to be carried away. These movements are 

 not to be considered as currents of water flowing now in this, 

 now in that direction. Just as root hairs take up fluids from the 

 soil and force them out into the adjacent cells, so each cell in the 

 path of transport is constantly receiving material and forcing it 

 out again into the surrounding tissue. 



32. Character of the Stem. — In order to comprehend the nature 

 of the work performed by the stem it will be necessary to ex- 

 amine its external form and its internal structure. While stems 

 vary greatly in character we may gain a general understanding 

 of their more important features by studying some woody twigs 

 or branches as they appear in winter (Fig. 39). The most strik- 

 ing features in such twigs are the buds, the leaf scars (see page 41), 

 lines of fine scars forming rings about the stems at varying inter- 

 vals, minute roundish or lense-like elevations (the lenticels), and 

 finally the character of the branching. The buds of the hickory, 

 horse chestnut, Norway maple, lilac, cherry, etc., are excellent 

 for study. In these buds, as in most examples, the outer part 

 consists of a series of leathery, closely overlapping scales or 

 modified leaves. These function to protect the delicate parts 



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