CHAPTER IV 

 THE MORPHOLOGY AND PHYSIOLOGY OF STEMS 



1. THE DISTINCTIVE CHARACTERISTICS OF STEMS 



STEMS are second only to leaves in prominence and im- 

 portance as a constituent of vegetation. They are dis- 

 tinguished by their tapering-cylindrical, continuous-branch- 

 ing, radiate-ascendant forms, so constructed as to support 

 and spread the leaves in the light. This is their primary 

 function, although, as with other plant parts, some kinds per- 

 form additional and even substitute functions. 



Foliage-supporting stems, even when performing the same 

 function, differ greatly in their external features. In shape, 

 their differences center in diverse degrees and methods of 

 branching, as will later be noted. In size, they range from 

 minute in small herbs, all the way up to the gigantic stature 

 of the famous California Redwoods (Sequoia gigantea), over 

 320 feet tall and nearly 30 feet through, or the Gum trees of 

 Australia (Eucalyptus amygdalina), even taller though not 

 so stout. In mere length, however, these stems are much 

 surpassed by the Rattan Palm, which clambers as a vine for 

 more than a thousand feet through the tropical woods. In 

 texture, all herbaceous stems, including the new growth on 

 trees, are soft-cellular like the leaves, being softest in water 

 plants, which are supported by their buoyancy in the water. 

 In trees, however, the stems become firm in various degrees 

 through softwood and hardwood, even to " iron wood," as 

 familiar in lignum vitse. In color herbaceous stems are green, 

 from presence of chlorenchyma, which aids the leaves in food 

 formation ; but older stems, which develop a thick protective 

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