28 GENERAL ARRANGEMENT OF PLANTS. 
growing vertically, is distinguished as the longitudinal system. 
It is in this direction that the fibres of which we have to treat 
are placed in the plant. The development and arrangement 
of these two systems produce three distinct forms of growth 
and of internal structure. 
Acrogens, or summit growers, so called from the growth of 
the stem taking place by the junction of the bases of the leaves 
at the top of the stem, as in Tree Ferns. Under this—used as 
a general term—cellular plants, such as Mosses, &c., are in- 
cluded; but none of them yield fibre, either for cordage or for 
textile purposes, though it is possible that some of the ferns 
contain fibre enough to form pulp for paper-makers. 
Endogens, or inside growers, are so called because the bun- 
dles of vessels and fibres proceed from the bases of the leaves 
into the cellular centre of the stem, and are thence. pushed 
outwards by the new growths, so that the outside of such stems, 
as of Palms, is harder than the inside. These plants have no 
regular bark which can be stripped off, and their leaves have 
the veins running parallel to each other. It is these leaves 
which abound in fibre, which may be separated by simple 
pressure and washing, as in the Pine-apple, Agave or American 
aloe, Plantain, and many others. In Palms, the structure of 
the leaves is too dense for the fibres to be separated so easily. 
Exogens, or outside growers, are so called from additions to 
their stems being made on the outside of the growth of for- 
mer years, as seen in the rings of wood on a transverse section 
of the trunk of any of the ordinary trees of Europe. There 
is also a distinct bark, of which the outer part is composed of 
cellular, but the inner contains the woody tissue. From this 
the fibres are separated for various economic purposes, usually 
by stripping off the bark and then steeping it in water, as with 
Flax and Hemp, Jute and Sunn. The leaves of Exogens havea 
reticulated or net-like, instead of a parallel venation. 
The above characters, taken from the parts of vegetation, 
are found to be accompanied by others equally characteristic, 
in the parts of fructification. Thus the spores of Acrogens, 
in germinating, are unaccompanied by anything like a leaf; 
the Endogens have a single seed-leaf, as may be seen in 
Wheat and other Cereals, as the Rice ; while Exogens, in sprout- 
ing display two of these seed-leaves, as in Peas and Beans. 
