57 
GARDENING AS A SCIENCE. 
VEGETABLE PHYSIOLOGY.— No. IIL 
Stems of the second class are now termed Endogenous, and the tribes of plants 
comprised in it are called Endogens. In its structure, this stem though perfect in 
itself, appears to be secondary, or less complete in its order than that of the 
Exogen ; for, as we read at No. 137, of Lindley's Elements of Botany, " the 
stem of Endogenous plants offers no absolute distinction of pith, medullary rays, 
wood, and bark." 
In respect to number — -if we assume De Candolle's computation of 1,000, as 
including all the tribes of the vegetable creation, — there are 144 endogens to 636 
exogens ; and in that number are comprised all the true grasses, and of course wheat, 
barley, rye, and oats, the sugar-cane, the amaryllis and liliaceous genera, and all the 
noble palm-trees. An accurate and minute physiologist, who, while he watches 
the external habits and growth of those plants which are at hand, investigates 
by dissection their internal structure, must observe, first, that the wood differs 
essentially from the wood of the exogenous class ; second, that the leaves have 
straight or at least parallel veins ; third, that the seed has but one proper lobe or 
cotyledon. We shall now notice these distinctive peculiarities in due order : — 
1st. The wood. In Exogens^ after the first year, layer upon layer is formed in 
succession upon, and exterior of the heart- wood, and interior, with respect to the 
bark. In Endogens., it might be said, that there exists no wood proper ; for even 
from the first developments of plants which subsequently become trees, the inner 
substance is, as it were, a mass of pith or cellular tissue, interspersed with scattered 
bundles of ligneous fibre. There is no central pith within a cylindrical sheath ; no 
system of convergent medullary rays ; no interposed, regular series of descending 
fibres ; no alburnum, liber, or bark. 
We will now assume, as an example, a plant which any one who has a small 
forcing-house can readily procure, and observe ; it is the common date-palm, raised 
from the seed (or stone) of the date sold by the grocers. We will now trace its 
growth from the first, for the seed germinates very freely in a pot of sandy loam 
and leaf-mould, particularly if the vessel be plunged in bottom-heat of 7^ degrees, 
and compare it with a few of the leading phenomena as they are described in that 
able article, " Endogens," of the Penny Cyclopaedia. 
Numbers of ligneous fibres, grouped in cords or masses, are arranged in 
circular order, and pass down the radicle or first root. A student should raise 
several seeds immediately, and dissect one as soon as he perceives the first develop- 
ment above soil ; he will then discover a root of amazing comparative length, 
which, ere the first leaf is an inch long, will perhaps have coiled itself twice round 
the bottom of a deep narrow garden-pot. If this radicle be cut across at its base, 
VOL. XI. NO. CXXIII. I 
