126 J. H. Priestley and Edith E. North 
a suberin lamella is deposited usually over the whole internal surface 
of the cell wall, including the Casparian strip, and lining every pit 
in the original membrane. The only new micro-chemical question 
that falls to be discussed therefore is the nature of the suberin lamella. 
In practice, this again proves a very complicated problem. 
In the first place are we justified in calling it a suberin lamella? 
Von Hohnel (li) first showed that substances of a corky nature were 
present in the endodermis in its secondary stage. He regarded these 
substances, found in periderm and endodermis, as one character¬ 
istic substance, suberin. In the endodermis he identified it by two 
reactions he regarded as characteristic, viz. (i) The cerin or cerinic 
acid reaction, obtained on treating the layer with strong oxidising 
agents such as Schulze’s macerating fluid (potassium chlorate in con¬ 
centrated nitric acid). This reaction is given very beautifully by 
strips of Potamogeton endodermis, especially if the cellulose is first 
removed with concentrated sulphuric acid. On gently warming the 
endodermis in the macerating fluid, the wavy walls collapse and give 
rise to yellow spherical drops, solidifying on cooling and soluble in 
fatty solvents. (2) The reaction with caustic potash. Warmed with 
the reagent three layers can be distinguished in the cell membranes, 
as in the case of periderm cells. These are, outermost the middle 
lamella, which on warming is recognised as a dark wavy line on 
either side of which can be seen the suberin lamella, and within 
this again von Hohnel noted the cellulose layer of the tertiary 
stage. 
The development of our knowledge of suberin since the days of 
von Hohnel has been traced elsewhere (Priestley (21)). We have re¬ 
examined the question in the light of this more recent work and 
conclude that there is evidence (1) that the “suberin lamella” is 
impregnated with condensation products of bodies like suberogenic 
acids, but not including the phellonic acid characteristic of the 
suberin of the cork oak; (2) that these products of fatty acids im¬ 
pregnate a basis which is not cellulose nor does it seem to be identical 
with the basal substances of the Casparian strip. 
Our evidence for these statements is as follows: 
(a) Evidence for “suberogenic acids." Using Van Wisselingh’s 
methods ( 33 ) sections of various roots were carefully warmed in con¬ 
centrated potash over a micro-burner. With periderm tissue the fats 
in the wall readily melted out into large balls, but in sections of 
roots the successful production of these balls was very difficult, 
probably because of the small amount of membrane under examina¬ 
tion. More success was obtained using the method with strips of 
