220 J. H. Priestley and R. M. Tupper-Carey 
the meristem walls would release the blue acid. This reaction was 
extremely clear and the contrast in the behaviour of meristem and 
older membranes well marked in longitudinal sections of the old 
root cut so as to pass transversely across the meristem of a young 
emerging rootlet. • 
These results suggested that the meristem wall behaved like 
an amphoteric protein, the isoelectric point of which is on the 
acid side of the normal sap reaction so that it behaves as an acid 
when first stained with Congo red, but on addition of io per cent, 
acetic acid, in a medium more acid than its isoelectric point, it 
behaves as a base (see Loeb(i0),(ii),(i2)). This point deserves noting 
because no cellulose or carbohydrate constituent of the membrane 
is likely to behave in such a manner; the actual interpretation of 
the staining reaction of proteins with congo red is still a matter for 
investigation, it is discussed again by Bayliss (in the 1921 edition of 
Bolles Lee (p. 125)). This possibly amphoteric behaviour has not 
been found in other roots growing in damp air, although much 
attention has been directed to the point, and the behaviour of 
sections to dyes and various salts carefully studied after previous 
immersion in a series of buffer solutions of definite Ph value. (See 
Cole (2) for general principle of these buffer mixtures and Loeb(i 3 ) 
for suggested value of subsequent reaction with silver or nickel 
salts, etc.) 
In all the roots examined the walls of the growing point were 
more resistant to concentrated sulphuric acid than the normal 
cellulose wall, dissolving in it very slowly indeed: they also with¬ 
stood boiling in concentrated potash. In a previous paper (Priestley 
and North (2i)), attention has been drawn to the resistance to con¬ 
centrated acid and alkali of the apical cells of the stem apex of 
Potamogeton perfoliatus L. In this plant the resistant character is 
retained by the walls of the layer around the plerome until it 
differentiates as the endodermis: in the rest of the tissue this 
character appears only to disappear as the cellulose reaction appears 
in the membranes. The presence of the resistant substance in a stem 
apex is attributed to the growth of the plant completely submerged 
under water, and this substance is thought to be similar to, if not 
identical with, the substance normally preceding the cellulose mem¬ 
brane at the root apex. 
There are reasons for assuming that nitrogen is present in the 
membrane at the stem apex of Potamogeton (Priestley and 
North (2i) p. 123) and therefore the effect of peptic acid and tryptic 
