CHAPTER VIII. 



THE STEM. 



Stems and branches are intended to support the 

 leaves, to hold them up above competitors, and out 

 of reach of browsing animals. The inflorescence 

 stalks^ modified stems, also display the flowers to the 

 best advantage. Besides this main object of placing 

 leaves or flowers in the most favourable position, there 

 are many other important functions which the stem 

 has to fulfil. It must be mechanically well con- 

 structed to endure the mere weight of the twigs and 

 leaves, as well as to stand against the uprooting effect 

 of a heavy wand. It must contain stores of food 

 material, to supply the buds when they develop in 

 spring. Its outside has to resist the attacks of fungus 

 and animal enemies, and must also prevent water 

 from escaping during its ascent to the leaves. The 

 increase in height of the Douglas Fir is sometimes 

 a foot in a year ; and, even though such trees as 

 the Horse-chestnut only grow a few inches in height, 

 still, this increase means a very much greater foliage 

 weight and foliage surface, and as these new leaves also 

 have to be supplied with water and food material, 

 there must be provision for an increase every year in 

 the diameter of the trunk. 



It is possible to give a rough idea of the structure 

 of a stem by a diagram, which will, at any rate, show 

 how the main necessities are arranged for. 



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