228 J. H. Priestley and R. M. Tupper-Carey 
4. The impermeability of the living meristem is also confirmed 
by its high resistance to the passage of an electric current. 
5. The function of the protoplasts in protoplasmic synthesis is 
evidence for their impermeability to water. 
6. The stem apex allows relatively free diffusion of water and 
solutes within the cuticle, the meristematic protoplasts at the apex 
staining readily with acid dyes. 
7. The difference in permeability of these meristems is due to 
the composition of the walls. In the stem apex they are of cellulose, 
in the root apex they are of unknown substances which are probably 
in part converted into cellulose by boiling with potash. 
8. The sap contained in the endodermal cylinder of the root is 
apparently more acid than the sap irrigating the stem apex. This 
fact may be correlated with the retention of colloidal electro¬ 
positive ions within the primary endodermis in explaining how in 
the root the apex obtains the amphoteric substances necessary to 
growth whilst the cortex receives very little. In the stem those same 
substances may bear a different charge, and escape more freely into 
the cortex as well as entering the apical meristem. The different 
staining capacities of the two apical meristems thus appear very 
significant. 
9. The relative ease with which the apical meristem of the stem 
is irrigated with substances, as compared with the supply of these 
substances to the root apex, is shown to suggest a physiological 
basis for the important morphological differences characteristic of 
these two growing points. 
10. The experimental results, summarised above, are in direct 
conflict with Coupin’s recent work on the function of the root apex. 
A critical examination of his experiments shows them to be inade¬ 
quate support for his theory that the growing point is the chief 
organ of the root for the absorption of water and solute. 
Botanical Department, 
University of Leeds. 
REFERENCES 
(1) Bayliss, W. M. Principles of General Physiology. London, 1915. 
(2) Cole. Practical Physiological Chemistry. 
(3) Coupin, Henri. Sur le pouvoir absorbant dn sommet des racines. 
Comptes Rendus, 168, p. 519. 1919. 
(4) - Sur le lieu d’absorption de l’eau par la racine. Comptes Rendus, 168, 
p. 1005. 1919. 
(5) - Sur F absorption des sels mineraux par le sommet de racine. Comptes 
Rendus, 169, pp. 242-244. 1919. 
