STRUCTURE OF ENDOGENOUS STEMS. 



103 



from the leaves, passes downwards in the softest part of the stem, 

 which is its interior ; but after proceeding for some distance in 

 this manner, it turns outwards, and interlaces itself with those 

 which were previously formed. In this manner, the lower part 

 of the exterior of a Palm stem becomes extremely hard ; partly 

 from the pressure from within, to which it is not elastic enough 

 to yield ; and partly from the constant interlacement of these new 

 fibres, which wind themselves in among the dense tangled mass 

 of the old, like roots seeking to pass through a stone wall. This 

 density is sometimes so great, as to resist the blow of a sharp 

 hatchet. 



142. The cellular portion of the stena, which in Exogens 

 was separated, by the first introduction of wood, into pith and 

 bark, here remains intermingled with the wood through the 

 whole duration of life, as is shown in the accompanying figure. 

 Each woody bundle 

 contains ducts and spiral 

 vessels, besides woody 

 fibre; and these are 

 arranged in such a man- 

 ner, that the spiral ves- 

 sels are on the side next 

 the centre, and are pro- 

 tected by the woody 

 fibre on the exterior. 

 The same elements, 

 therefore, exist in this 

 stem, as in that jof the 

 Exogen ; but they differ 



in their mode of ar- FlG - 52. HORIZONTAL AND VERTICAL SECTION OF THK 

 STEM OP AN ENDOQEN, showing the bundles of ducts, 



rangement. From their woody fibre, and spiral vessels, irregularly disposed 

 V i , ,1 through the whole stem, a, a, portions of cellular 



peculiar structure, they tissue * 6 , 6 , 6piral vessels ; c , e , dotted ducts ; *,d, 

 increase very little in woody fibre. 



diameter, the hardness of the exterior not permitting their 

 enlargement. The consequence of this is, that there is a limit 

 to their age ; for the continual addition of new woody bundles 

 to the interior, so much compresses those which were previously 



