GARDENING AS A SCIENCE. 
35 
their position is regular, and opposite ; and the future developments are, in a great 
degree, two -fold and distinct. 
The following positions are extracted from the Cyclopaedia, though of 
necessity somewhat abbreviated : — 
" 1. As soon as germination commences, fitie ligneous cords proceed from the 
cotyledons towards the radicles from the opposite sides of the young stem meeting 
in the centre of the embryo. 
" In this first position we perceive the earliest development of the fibrous 
woody matter of the root, which fibres are accompanied with a certain quantity 
of interposed cellular tissue." If then these two-fold developments are propelled 
from the seed by the excited vital principle, that seed or embryon must have 
comprised their elementary rudiments. 
" 2. The plumule or rudimentary stem becomes organized, and, having 
lengthened, forms upon its surface one, two, or more true leaves, which gradually 
expand into thin plates of cellular substance traversed by ligneous cords or veins 
converging at the point of the origin of the leaves. If the interior of the young 
plant be now examined, it will be found that more ligneous cords have been added 
from the base of the new leaves down to the cotyledons, where they have formed 
a junction with the first wood, and have served to thicken the woody matter 
developed upon the first growth." 
" Those ligneous cords which proceed from the base of the leaves do not unite 
with the centre of the stem, but pass down parallel with the outside, and leave a 
small space of cellular tissue in the middle." 
We hereupon remark, that in this second position, the Physiologist lays the 
foundation of his theory, namely, that the woody matter of Exogens proceeds from 
the leaves to the roots in parallel lines — or, in other words, that the leaves generate 
wood. Now", it is quite certain, that leaves are formed at a very early stage after 
germination, before ligneous fibres become distinctly traceable ; and if the hypo- 
thesis of Liebig be correct, that the absorption of carbonic acid from the atmosphere 
is one of the primary offices of the leaves, the theory acquires substance. Carbonic 
acid is formed by a union of oxygen gas, during combustion, with the base of 
charcoal : it also exists abundantly in chalk, and is developed in every act of rapid 
or slow combustion. As the air therefore must of necessity abound with this 
gas, it is reasonable to infer, that leaves absorb a portion of it. And as, moreover, 
fibres may be traced at the base of every leaf, and be proved to pass into the stem, 
we are further inclined to consider this connexion with the fibres of the stem 
sufficiently established : but we yet suggest the admission that the office of the 
leaves is nutrimental, not creative, the rudiments of leaf, fibre, and cellular tissue, 
being present in the plumule at the moment of its expansion from the embryo. 
" 3. The stem goes on lengthening, and forming new leaves : from each leaf there 
may be again traced a formation of woody matter disposed cylindrically, as before, 
and uniting with that previously formed, a cylinder of cellular substance being left 
