CHAPTER III 



The Stem 



The stem is the common support of the 

 different parts of the plant which, if it is only 

 to last one year, is called annual or herbaceous. 

 Such is the case of the potato, parsnip or 

 parsley, and of all those plants which from 

 their weak substance are called herbs. If 

 destined to last for a greater or less number 

 of years, being formed of strong wood, the 

 growth is called ligneous, as in the case of trees. 

 Let us cut very neatly through some 

 ligneous stem — for instance, the stem of an 

 oak. We shall perceive three parts — in the 

 centre the pith, very slightly developed ; 

 round the pith the wood ; and lastly the bark 

 outside. With a little attention you will 

 recognise that the wood consists of concentric 

 layers, outlined on the section of the stem 

 by a series of circles, which have the pith 

 for a common centre. These layers are called 

 ligneous zones, or annual layers, because one 



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