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. 



