86 GENERAL BOTANY 



stem (and the roots too) of the former do not increase 

 in thickness, and have no true bark as in the latter. 

 But we can easily learn more than this. If we examine 

 the stem of any small monocotyledon, e.g. Cholam, 

 Wheat, Paddy or a Lily, more closely, we find that 

 it is composed of numerous strands of fairly tough 

 material imbedded in a much softer ground-tissue, 

 which can easily be torn apart with the fingers to 

 separate the strands. This is quite different from the 

 stem of a dicotyledon, where (except in a very few 

 cases) there is a solid cylinder of wood. These strands 

 run into the leaves and there form the veins. Those 

 nearer the surface are closer together, and form a hard 

 casing, but not a true bark. These strands are called 

 vascular bundles and are composed of six main kinds 

 of elements : 



(1) Continuous tubes with fairly thick walls, in which 

 there are thinner places (pits, not holes). These are 

 called vessels, and it is through them mainly that water 

 passes up from the roots to the leaves. 



(2) Shorter closed tubes with pointed ends and much 

 the same kind of walls. These are called tracheids, and 

 share in the conduction of water up the plant. 



(3) Long thin elements, like tracheids, but with 

 excessively thick walls so that there is little or no space 

 inside ; these are fibres, and their function is to add 

 strength to the vascular bundle, and the plant generally., 

 They usually form a sheath round the bundle and in old 

 decaying stems of Palms one can see the black fibrous, 

 sheaths, often after the insides have decayed away. 

 Individually the fibres are really short (seldom more 

 than one-eighth inch) but they often form strong strands 



