
70 KIDD’S OWN JOURNAL. 

POPULAR SCIENCE. 
a 
VEGETABLE PHYSIOLOGY.—No. III. 
THE NUTRITION AND GROWTH OF PLANTS. 
BEFORE PROCEEDING TO THE SUBJECT 
of Nutrition and Growth, a few remarks on 
the structure of the stem and root of plants 
are necessary. 
The stem, or ascending axis of the plant, 
is separated from the root by the collar or 
neck, and is distinguished from it by having 
a provision for the development of leaf-buds 
on its surface. As ageneral rule, the former 
rises into the air, bearing leaves and flowers, 
while the latter ramifies in the soil. Both 
organs are composed of the two classes of 
tissue described in our last. 
Taking the stem of a tree or shrub as an 
example, we find in the centre a quantity of 
soft matter, known as the pith ; composed 
entirely of cellular tissue, and occupying in 
the young stem a very great space. Next to 
this is a ring of cells and vessels,—not quite 
wood, and not altogether pith. Then a ring 
of wood, having very few cells, composed 
almost entirely of the spindle-shaped or 
woody vessels ; and outside this, the bark, 
which is almost altogether cellular. We have 
supposed that the portion of the stem under 
examination is only of one year’s growth; for 
every year a fresh circle of wood is developed, 
giving that annulated appearance to a cross- 
section of timber, by which the age of the 
tree may be told by the merest tyro. This 
description applies to all British plants which 
have a woody stem,—as trees and shrubs. 
In the palm and cane tribes, it is different. 
No pith and concentric circles are visible, 
but a confused mixture of cells and vessels 
throughout the whole stem. ‘The root differs 
but little from the stem in structure, save 
that at the extreme point it is uncovered by 
bark or membrane of any kind; presenting a 
sponge-like mass of cells, whose office it is to 
take up the liquid nutriment in the soil. 
In order to have some idea of the mystery 
of growth, let us trace the fluid from the roots, 
in its progress up the stem, to the leaves, and 
down again, until it forms wood, bark, leaves, 
and flowers. 
The plant being placed in favorable circum- 
stances as regards moisture in the soil, and 
heat and light in the surrounding air, the 
roots take up the proper nutriment in the 
form of a fluid, by means of their sponge-like 
extremities, and from thence they deliver it 
to the stem. In the present state the sap is 
thin, and unfit for nourishment. Through the 
soft wood this crude sap proceeds to the leaves, 
and courses along their upper surface, where 
under the agency of heat and light it parts 
with a considerable quantity of its moisture ; 
becoming the thickened and elaborated sap. 



The change here produced is the fixation of 
carbon and hydrogen, accompanied by the 
liberation of pure oxygen. Descending to 
the lower surface of the leaf, a further addition 
of carbon is received, owing to the decom- 
position of carbonic acid gas. The sap now 
enters the vascular and cellular tissues of the 
bark, and commences a downward journey, 
nourishing the parts as it goes on. 
This fluid is received by the woody fibres, 
and leaves a thickening deposit on their 
walls, which deposit afterwards obliterates 
all passage, transforming them into tough 
little rods. The same thickening process 
goes on in cells, till they become, in like 
manner, solid masses. In this manner, dis- 
tributing its benefits as it flows, the sap, 
when comparatively exhausted, at length 
reaches the root, which, abstracting what is 
necessary for its increasing vigor, rejects the 
worthless residue. This elaborated sap is 
sometimes clear and transparent, though 
oftentimes colored and milky. It is by no 
means an easy matter to observe the flow of 
the sap, owing to the delicacy of the vegetable 
tissue, and the often colorless nature of the 
fluid itself; but, in a few plants, it has been 
noticed, and among these the Caoutchouc 
tree, the Celandine, and the Euphorbia; all 
of which have it more or less opaque and 
colored. It is between the newest layer of 
wood, and the inside bark, that the formation 
of new wood takes place; and there we have 
a quantity of fluid not unlike mucilage. A 
brief consideration of the important opera- 
tions carried on here, may prove not unin- 
teresting. 
This thick mucilaginous fluid is made up 
of the elaborated sap, or secretions from the 
adjacent cells. Under the force of one of 
those inscrutable laws which regulate life,— 
vegetable as well as animal,—a change takes 
place in the consistency .of this fluid. It 
becomes granular, each granule becomes a 
cavity, each cavity gives birth to other 
granules, and these secondary granules be- 
come in their turn cavities. Enlarging and 
strengthening, they become covered with a 
proper membrane, and form regular woody 
cells or vessels. At first they are rounded, 
and in that state carry on the functions of 
nutrition and reproduction. But they gradu- 
ally lengthen into the spindle shape; after 
which they become thickened by the depo- 
sition of a hard substance in their interior,— 
ultimately obliterating all opening, and form- 
ing regular woody fibre. 
From what has now been stated, the reader 
will have a slight notion of how wood is 
developed; but as cellular tissue is of much 
more frequent occurrence in the vegetable 
kingdom, than vascular—seeing that many 
plants are entirely without the latter, while 
it is impossible for any to exist without the 


