33 
GARDENING AS A SCIENCE. ■ 
VEGETABLE PHYSIOLOGY.— No. IL 
It appears certain, whatever be the structure of a plant, that there is a point 
of union between the root or the descending organ, and the stem, — the part or 
parts which ascend, and luxuriate in solar light,^ — at which two systems of vessels 
unite (inosculate) and distribute to each, in opposite directions, the fluids required 
by each. This point of union is called the neck (colla) or collar. All that part 
through which the sap ascends, and from which buds, branches, and leaves proceed, 
is therefore with propriety called the Stem. 
A distinction, however, might be made, inasmuch as the main ascending 
portion of trees and shrubs is manifestly the stem, in the common acceptation of 
the word ; but physiological botany of the modern school admits of no such 
distinction : it indeed sanctions the term woody stem ; but it claims the right to 
consider as stem, every central portion which is above the collar of union ; and 
thus the bulb in the tulip, the amaryllis and crocus, is a stem, the base of which 
is the collar, whence the fibrous roots pass into the earth. 
This being admitted, we appeal to the authority (the most modern) of 
«'Lindley''s Physiology"" for the following positions : — 
" The stem varies in structure in four principal ways. First, as being formed 
by successive additions to the outside of the wood, — it is then called 'Exogenous^ 
(derived from the Greek word efco, without or outside, and ye^co or yez^eti^, to 
produce ; second, by successive additions to its centre, when it is called Endo- 
genous (from evhov^ within) ; third, by the union of the bases of leaves, or by 
addition to the point (aKpov,) whence the term Acrogenous ; and fourth, when a 
stem has the structure of an Endogen, and the root that of the stem of Exogens, 
called Dictogens, (from AtKa, in two ways). 
These four classes will be noticed in due order ; and first, Exogenous Stems. 
When a seed with two seed-lobes, is excited, it first protrudes a root, by which it 
fixes the future plant in its medium of nutrition — the soil : — it then produces the 
seed-leaves and the rudiment of the ascending stem called the plumule^ con- 
sisting chiefly of soft, juicy cells or tissue, among which pass downward and 
upward — that is, in a vertical direction — a number of delicate fibres, which are the 
rudiments of the fibrous system that subsequently becomes the basis of solid wood. 
If a tender stem of any young seedHng shrub or tree, be cut lengthway and across 
by a delicate instrument, the truth of these assertions will be clearly established. 
There will be found a marked separation between the fibrous and cellular tissues ; 
the two-fold arrangement being in a great degree symmetrical. 
This is more obviously discernible in trees, wherein there is a regular progressive 
deposition of woody matter : but it is not less true in plants of herbaceous families, 
wherein the stem, though it become not woody in the proper sense, yet exhibits 
VOL. XI. NO. CXXII. F 
