CHAP. TI. 



ENDOGENOUS STEMS. 



'81 



§ 2. Of the Endogenous Structure. 



o 



41 



Plants of an arborescent habit having this structure being 

 almost exclusively extra-European, and most of them being 

 natives onlj- of the tropics, botanists have had fewer opppor- 

 tunities of examining them, and, consequently, our knowledge 

 concerning them is far more limited. It is, therefore, pro- 

 bable that in this department of the subject there will be 

 hereafter much to add and correct. 



In Endogenous plants the vascular 

 and cellular systems are as distinct as 

 in Exogenous, but they are differently 

 arranged. The cellular system, instead 

 of being distinguishable into pith, bark, 

 and medullary rays, is a uniform mass, 

 in which the vascular system lies im- 

 bedded in the form of thick fibres, 

 having no tendency to collect into zones or wedges resembling 

 wood. The fibrous bundles consist of woody tissue, enclosing 

 spiral or other vessels. 



The following is an explanation of the opinions generally 

 entertained concerning the formation of an Endogenous stem. 

 Its diameter is supposed to be increased by the constant addition 

 of fibrous bundles to the centre, whence the name; those bundles 

 displace such as are previously formed, pushing them out- 



o 



