430 
VEGETABLE ORGANISATION. 
evident that the secondary vesicles will be more compressed towards 
the centre than at the circumference, and that, consequently, a trans¬ 
verse section will exhibit each of these secondary cells in the form of a 
wedge. If eight vesicles grow in a longitudinal direction, without 
giving rise to other vesicles within them, we shall then have an orga¬ 
nisation similar to that of the long stalk which supports the flower of 
the Nymphceci alba, or white water-lily—a monocotyledonous plant. 
Each of these vesicles will form an empty canal, of which a longi¬ 
tudinal section will present a three-sided prism, and which will extend 
from the base to the summit of the flower-stalk ; but, if within each 
secondary cell a certain number of tertiary vesicles be developed, so as 
to form cells of a considerable size, and nearly empty, we shall then 
have the structure of the central part of certain trunks of the mono¬ 
cotyledons, and also that of the pith, as it occurs in some of the stems 
of the dicotyledons. Now if, instead of vesicles thus developed, parallel 
and concentric cells are formed, we shall have a commencement of con¬ 
centric layers; and other vessels being developed in the interstitial 
spaces in a longitudinal direction, so as to form tubes or vessels, a 
transverse section will exhibit the perfect development of the con¬ 
centric vascular tissue. If the cells, instead of loose hexagonal cells, 
give rise to other vesicles pressed one against the other, and developed 
on the coats of more internal cells, which are encased in, and line com¬ 
pletely, the cavity of those in which they are formed, then we shall 
have the most complicated organisation of the stem of a dicotyledonous 
plant, with its encased and concentric layers and its medullary rays, 
which are nothing else than the interstices of the secondary cells, or 
rather the junctions of their sides, in which vesicles have been deve¬ 
loped in a horizontal direction, forming tubes or vessels running from 
the centre of the stem towards the circumference. 
“ Branches are nothing more than the divisions of the stem, and may 
be conceived to be formed by the progressive development of cells and 
tubes in a manner altogether similar—a generating vesicle gradually 
developing other vesicles upon its internal membrane, and the growth 
taking place as in the former instance. 
“ Leaves consist of a cuticle or transparent film of cellular texture, 
enclosing a parenchyma or pulp, also of cellular tissue, and usually of 
a green colour, and fibres, of which the nerves and veins of the leaf are 
chiefly composed. These fibres communicate with each other, and are 
ramifications from the midrib. In the monocotyledonous plants, the 
nerves are for the most part parallel, or nearly so, extending from the 
leaf-stalk to the apex of the leaf in a longitudinal direction, and rarely 
branched, but communicating with each other by short transverse ribs, 
