Physiological Studies in Plant Anatomy 127 
Potamogeton endodermis. The balls thus obtained, with iodine and 
potassium iodide and dilute sulphuric acid, or with chlorzinc-iodine, 
stained dark brown or reddish brown but never the colour of the 
similar balls obtained from periderm, which turn red violet in colour 
owing to the potassium phellonate they contain. 
Strips of Potamogeton endodermis were then heated in anhy¬ 
drous glycerine. Fusible products were obtained at 280° C., the 
temperature at which Van Wisselingh obtained similar results in the 
case of the periderm of Salix caprea and Ilex aquifolia. On heat¬ 
ing in glycerine, after three days maceration in 50 per cent, potash, 
the contents fused out of the suberin lamellae at a temperature 
of 95°-ioo°C. The balls of potassium soaps of organic acids obtained 
by these methods never gave the phellonic acid reaction with 
iodine reagents. The absence of phellonic acid was further confirmed 
by boiling considerable quantities of the Potamogeton strips upon a 
microscope slide first in potash and then in alcohol. The potassium 
soaps formed are soluble in alcohol and as the alcohol gradually boils 
away are left concentrated in one small portion of the preparation. 
The relatively large concentration of fatty substances thus obtained 
gave no phellonate reactions. 
Finally, using the methods of Gilson ( 9 ), a considerable bulk of the 
endodermis was boiled with alcoholic potash. On concentrating the 
solution thus obtained, a small quantity of a crystalline precipitate 
formed on cooling. This precipitate did not give the reactions of 
phellonic acid, and its further characterisation awaits fuller macro¬ 
chemical investigation. 
The results obtained thus far show that the suberin lamella un¬ 
doubtedly contains substances of the general type of the suberogenic 
acids, but in no case so far examined has phellonic acid been found 
amongst these acids. In view of this conclusion it is important to 
note that we can confirm Kroemer(i 3 ) and Mylius(iB) as to the dis¬ 
tinctly different behaviour to various reagents of suberin lamella and 
Casparian strips. Phloroglucin (or catechin) followed by hydro¬ 
chloric acid stains the Casparian strip red and the suberin lamella 
yellow, thus indicating that the suberin layer, unlike the Casparian 
strip, is not always impregnated with substances giving reactions 
characteristic of lignin. 
Dimethylaminoazobenzene (in an alcohol glycerine solution) fol¬ 
lowed by concentrated hydrochloric acid stains preparations which 
have previously been soaked in 1 in 300 hydrochloric acid, the 
Casparian strip becoming red, the suberin layer yellow. This reaction 
was obtained most beautifully with the rhizome of Pteridium 
