222 J. H. Priestley and R. M. Tupper-Carey 
the cellulose appears to be formed actually in the meristematic 
region. 
No further relevant information has been obtained as to the 
nature of the substances that precede cellulose in the membranes 
in the meristematic region. Sections of the root apex were heated 
with concentrated caustic potash in sealed tubes in an oil bath to 
a temperature of i8o° C. and subsequently tested for chitosan with 
20 per cent. H 2 S 0 4 and dilute iodine in potassium iodide (van 
Wisselingh( 30 )) also with bromine water (Zemplen( 3 i)). A strong 
reddish-purple coloration was obtained with the dilute iodine 
when the section was left in the reagent for some hours, the colour 
approximating very closely to that given immediately by chitosan 
(or mycosine) prepared from Polyporus betulinus and Psalliota cam- 
pestris by Miss L. M. Woffenden according to Gilson’s method (8). 
Comparison with the behaviour of filter paper similarly fused at 
i8o° and then left in the acidified dilute iodine showed that this 
delayed reaction was given by the cellulose wall and could not 
be regarded as any indication of the presence of chitosan, but was 
probably due to the presence of cellulose in the meristematic region 
as the result of the previous treatment. This reaction, therefore, 
supplies no evidence for the existence of chitin in the wall prior to 
its fusion with alkali. 
Though we are still without evidence as to the exact nature 
of the cell wall at the root apex, observation and experiment show 
clearly that the difference between the permeability of the apices 
of stem and root is due to the difference in composition of the 
intervening walls. The importance of this conclusion in relation to 
the morphology of stem and root is discussed in the next section. 
(4) Morphological Consequences of the Different Permeabilities 
of Apical Meristems 
Results recorded in other papers have shown that the apical 
meristems of root and stem are dependent upon supplies received 
from the vascular system. Some experiments upon the quantitative 
growth of roots (Priestley and Evershed( 23 )), have led us to antici¬ 
pate that should the supply of solute fall below a certain minimal 
value the rate of growth of the meristematic tissue will be seriously 
affected. 
On comparing the growing points of stem and root from this 
standpoint and taking into account their relative permeabilities it 
will be clear that the area supplied will be very different in the two 
