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, thickness 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 arrangement 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 approach the square form.
All typical cortical parenchyma cells have uniformly thickened 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., according 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.
PLATE 51
Parenchyma Cells