ENDOGENOUS.—ACROGENOUS. 79 
fibro-vascular system arranged vertically in this in the form of 
separate bundles, f, which have no tendency to form concentric 
Fia. 176. Fie. 177. 
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Fig. 176. Transverse section of an Oak-branch six years old. m. The me- 
dulla or pith. c,c. The bark. 7. The wood, arranged in concentric layers. 
b, Medullary rays. —— Fig. 177. Transverse section of the stem of a Palm. 
m. The parenchyma. j.The fibro-vascular bundles. 0, The rindor false 
bark, 
layers of wood ; the whole being covered externally by a fibrous 
and parenchymatous layer, b, which, as will be hereafter seen, 
is formed essentially by the ends 
of the fibro-vascular bundles, and Fic. 178. 
which is termed the false bark or 
rind. This structure is called En- 
dogenous (from two Greek words 
signifying inside growers), as such 
stems grow by the addition of 
new fibro-vascular bundles which 
are at first directed towards their 
interior. These two structures, 
the Exogenous and Endogenous, 
are characteristic of Flowering 
plants. 
If we now turn our attention 
to the Cryptogamia, and make a 
transverse section of a Tree-fern 
(fig. 178), we observe the centre, Fig, bes ce a penton of ie 
m, to be either hollow or filled tnatous cells, which are wanting in 
with parenchyma, the fibro-vas- the centre. v, ¥, v. Fibro-vascular 
cular bundles being arranged in Puniles. e. Rind. 
irregular sinuous plates around it, 
v, v, v, and forming a continuous or interrupted circle near the 
circumference, which consists of a rind, e, inseparable from the 
wood beneath. This structure is termed Acrogenous (from two 
Greek words signifying swmmit growers), because the fibro-vascu- 
lar bundles of such a stem grow oniy by additions to their apex. 
