CONDUCTING TISSUE 147 
and endosperm, conduct in all directions—upward, downward, 
and laterally. The direction of conduction depends upon the 
needs of the different cells forming the plant. The fluids pass 
from the cell with an abundance of cell sap to the cell with less 
cell sap. In this wall all cells are provided with food. 
Parenchyma cells conduct water absorbed by the roots and 
soluble carbohydrate material chiefly. 
The walls of all the different types of parenchyma cells are 
composed of cellulose with the exception of the wood parenchyma 
cells, the walls of which are lignified. The end walls of non- 
branched parenchyma cells and the cell terminations of branched 
cells are very blunt. 
CORTICAL PARENCHYMA 
Cortical parenchyma (Plate 51) differs greatly in size, thick- 
ness of the walls, and arrangement. A study of the longitudinal 
sections of different parts of medicinal plants reveals the fact 
that the cortical parenchyma cells form superimposed layers 
in which the end walls are either parallel, in which case the 
arrangement resembles that of several rows of boxes standing 
on end, or the end walls of the cells alternate with each other, 
in which case the arrangement is similar to that of the arrange- 
ment of the bricks in a building. 
In certain plants the cortical parenchyma cells are long and 
narrow and rectangular in shape, while in other plants the cells, 
although still rectangular in outline, are very broad and ap- 
proach the square form. 
All typical cortical parenchyma cells have uniformly thick- 
ened non-pitted walls. In most barks the parenchyma cells 
beneath the bark are elongated tangentially, but are very narrow 
radially. The cells are always arranged around intercellular 
spaces, which vary from triangular, quadrangular, etc., accord- 
ing to the number of cells bordering the intercellular space. 
PITH PARENCHYMA 
Pith parenchyma (Plate 52) differs from cortical parenchyma 
cells chiefly in the character of the walls, which are usually thicker 
and always pitted. 
