CHAP. II. 
ENDOGENOUS STEMS. 
107 
which forms the woody bundles of Endogens. In the latter 
each woody bundle is, when divided transversely, described by 
Mohl as consisting of the following parts (fig. 45.) : 
45 
a. Thick-sided "woody tissue (^cellulcB librf). 
b. Bothrenchyma (vasa porosa). 
c. Thin-sided parenchyma (vasa propria'). 
e. A variety of bothrenchymatoiis tissue (cellules lignipunctatcB'). 
f. Spiral vessels. 
But this is quite unlike the anatomy of the smaller portions 
of woody tissue in Exogens, in which there is no such ar- 
rangement of woody tissue, so called vasa propria, or spiral 
vessels. 
Endogens have no bark. They have a cortical integument 
composed of an epiphloeum and an inner layer, analogous per- 
haps to liber ; and the woody part of which, according to 
Mohl, is formed in Palms by the introduction of the ends of 
the woody arcs of the stem. In Tamus elephantipes the epi- 
phloeum acquires the nature of cork, but splits into pyramidal 
laminated areae. This approximates the cortical integument 
of Endogens very little to true bark, which is essentially cha- 
racterized by being separable from the wood ; and having its 
woody tissue parallel with that of the stem, and formed alto- 
gether in an independent, though parallel, direction. 
