ENDOGENOUS OR MONOCOTTLEDONOUS STEM. 51 



cells, covered by an epidermis, e. The peripherical portion, /, differs 

 from true bark, in not being separable from the rest of the tissue. It 

 has received the name of false bark, and consists of the epidermal cells, 



/ 



v/i M. 



e, and what has been called the cortical integument, I. This portion 

 of the stem is often very inconspicuous, but sometimes it is much 

 developed as in Testudinaria elephantipes, in which it is rugged, and 

 is formed of a substance resembling cork in many respects. 



93. Mohl states that, in the stem of a Palm, there may be distin- 

 guished a central region, a fibrous layer, and a cortical region; and 

 the same divisions are pointed out by Henfrey in the stem of Spar- 

 ganiiun ramosum and other monocotyledons. The central portion, 

 representing the pith of dicotyledons, consists in Sparganium of 

 spherical cells containing starch, while the cortical or outer portion is 

 formed by irregular cells, which are usually destitute of starch. 



94. It was at one time supposed that the woody portion of these 

 stems was increased by additions to the centre, so that the first-formed 

 fibres were gradually pushed towards the circumference by those which 

 succeeded them, in the manner represented in fig. 114, 1: hence 

 the term Endogenous (bSov, within, and ygj/i/aa, I produce), meaning 

 internal growth. But Mohl showed that this was not strictly correct. 

 For although the fibres connected with the leaves, in the first instance, 

 are directed towards the centre, and are therefore always internal to 

 those previously formed, yet, when they are traced downwards, they are 



Fig. 112. Horizontal section of a vascular bundle from the stem of a Palm (Coryphafl-igida). 

 t, Tracheae, or spiral vessels, v p, Large porous vessels. , Cells or utricles of various kinds 

 surrounding the vessels, and forming the parenchyma. I, Laticiferous vessels. /, Fibres analo- 

 gous to those of liber, thickened by concentric deposits. 



Fig. 113. Transverse section of part of the stem of a Palm (Astrocaryum Murumura). m, 

 Central or medullary portion in which the woody bundles are distant and scattered, b, External 

 woody portion, where the fibres are numerous and densely aggregated, so as to form a dark 

 zone. /, Paler circle of more slender and less compact fibres, which may be considered as analo- 

 gous to liber, e, Cellular epidermal portion. 



