THE ANATOMY OF STEMS. 251 



pearances of the internal mass are all found to con- 

 sist of cellular substance, with vessels running through 

 it, and anastomosing in a variety of directions. Many 

 of these plants have no stem ; but among those which 

 possess it, in some it is solid, in others hollow ; and 

 in the latter case, the cavity is often partially lined 

 with a very lax, dry, cellular web. A conspicuous 

 root is rare ; and, when it exists, consists of a few 

 small radical fibres only. Scarcely any facts are yet 

 known respecting the developement and growth of 

 this description of stem. 



Monocotyledonous Stems. 



These are more complex in their structure than the 

 preceding ; being composed of two distinct parts, lig- 

 neous and cellular, which assuming a determinate 

 character, enable these stems to be readily distinguish- 

 ed, even by the naked eye. They are either solid 

 or tubular, and as there is some difference in the ar- 

 rangement of the parts in these varieties, we shall ex- 

 amine them separately. 



If a solid monocotyledonous stem, that of a Palm, 

 for example, be cut, either longitudinally or transverse- 

 ly, it is seen to consist of an epidermis enclosing lig- 

 neous bundles or cords, more or less symmetrically 

 distributed in a parenchyma or medullary substance. 

 If the section be longitudinal, these ligneous cords are 

 observed to run lengthwise, and extend from the buse 

 to the apex of the stem ; sometimes in straight lines ; 

 but occasionally assuming a zigzag direction, so as to 

 touch each other at different distances ; closer togeth- 

 er and firmer towards the circumference of the stem, 

 and more apart and softer as they approach its centre. 

 It lie section be transverse, the divided extremities 

 of the ligneous bundles appear like spots, which are 



