ENDOGENOUS STRUCTURE. Si 
209. That portion of the stem which serves this important 
purpose is the alburnum (203). Through its ducts and fibres 
the sap is elevated to the leaves, with the vessels of which they 
communicate. Having been there elaborated by exhalation and 
decomposition into a certain nutritious fluid called Jatez, it de- 
scends by the laticiferous tissues of the liber. Of this descend- 
ing sap a part is carried inward from the bark by the medullary 
rays, and thus diffused through the whole stem; the remainder 
descends to the roots, and is in the same manner diffused 
through their substance, both for their nourishment, and for the 
purpose of maintaining the conditions requisite for endosmose 
(159, a). 
§3. OF THE ENDOGENOUS STRUCTURE. 
210. In the endogenous stem there is no distinction of pith, 
wood, and bark, nor does a cross-section exhibit any concentric 
arrangement of annual layers. (Fig. 26; 3, 5.) 
211. It is composed of the same tissues and vessels as that 
of the exogen, that is, of cellular tissue, woody fibre, spiral ves- 
sels, and ducts; the first existing equally in all parts of the 
stem, and the rest imbedded in it in the form of bundles. 
212. Each bundle consists of one or more ducts, with spiral 
vessels adjoining their zmer side next the centre of the stem, . 
and woody fibres on their outer side, as in the exogen. 
a. A new set of these bundles is formed annmally, or oftener, proceeding from 
the leaves and passing downwards in the central parts of the stem, where the cel- 
lular tissue is most abundant and soft. After descending awhile in this manner, 
they turn outwards, and interlace themselves with those which were previously 
formed. Hence the lower and outer portions of the palms, and other endogens, 
become exceedingly dense and hard, even so as to resist the stroke of the axe. 
b. The age of most endogenous trees, as the palms, would seem to be limited 
by this peculiarity of growth. The stem at length becomes incapable of further 
increase in diameter, and the lower portions of it so densely filled with the de- 
scending fibres as to become impervious to all succeeding ones, and the tree 
languishes and dies. 
e Endogenous stems, both herbaceous and woody, are often hollow, with solid 
joints ; as in the grasses and bamboo. 
