48 THE VEGETABLE WORLD. 
in vain for the central pith, the concentric zones, the radiating lines, 
which so plainly characterise the wood of our indigenous trees. 
We should see, on a groundwork of palish colour, little spots of 
a deeper tint, formed by a more solid tissue. These little rounded 
or half-moon shaped spots are more numerous, more crowded, 
higher coloured, and in general larger towards the circumference 
of the stem than they are in the central part. This stem is called 
Endogenous, from evdov, “within,” and yevvaw, “I produce.” This 
stem, therefore, appears at first-sight formed of two descriptions of 
tissue, one rather soft and pulpy, forming the bulk, so to speak, the 
other very solid, forming little islets in the interior of the former. 
Microscopic examination has shown us that the first of these 
tissues is exclusively formed of cells, and may be compared to the 
pith of our indigenous trees. It is traversed also by vascular 
bundles or very tough fibres, the tortuous course of which may be 
traced theoretically by the help of Fig. 55, in which letters a, B, © ? 
represent the different interlacings of these fillets in the middle of 
the pith. The fibrous bundles which traverse the stem of the — 
Palm and other trees belonging to the same natural group, present 
arrangements which are very interesting to understand. The 
anatomical structure of each of them does not appear to be alike — 
through their whole length ; it seems to become more simple the — 
farther they are distant from the point where they leave the ste™ 
to pass into the leaves. In this higher part, at the end of its | 
course, the fibrous bundle of which we speak is invested with the 
characteristic structure of the stems of our indigenous trees 
including the medullary sheath ; presenting, in fact, trache®, 
punctated and striated vessels of a greater or less size, ligneous — 
fibres, and other peculiarities of indigenous stems. 
The Tree ferns of warm climates approach in their appearance 
much nearer to Palms than to our indigenous trees. Their slendet 
trunks, simple and branchless, and of nearly equal thickness from 
the base to the summit, support at a great height a tuft of leaves 
Nevertheless, Ferns differ much from Palms in their internal 
structure. Round an abundant pith voluminous vascular bundles - 
are drawn out, showing in the transverse section of the stem 4 
winding form, more or less irregular and hieroglyphic, and groul e 
