138 J. H. Priestley and Edith E. North 
from the inner margin of the Casparian strip, and is usually deposited 
all over the inner surface of the cell. 
11. This suberin lamella is impregnated by substances, similar 
to the derivatives of suberogenic acids found in the suberin lamella 
of normal periderm, but on saponification no salts of phellonic acid 
can be identified. 
12. The impregnating substances do not give the same staining 
reactions as those of the Casparian strip. 
13. Evidence is advanced for the presence of a basal substance 
of unknown composition in the suberin lamella, but differing from 
that occasionally present in the Casparian strip in its solubility in 
strong sulphuric acid. The simplest tentative assumption is that this 
substance is a carbohydrate, a more resistant cellulose derivative, 
allied to the modified cellulose-like substance deposited in the internal 
layers of the tertiary stage endodermis in Potamogeton. 
14. The suberin lamella renders the secondary endodermis re¬ 
latively very impermeable both to water and solutes, except when 
passage cells are present. Experimental evidence for this conclusion 
is given. 
15. The conclusions reached in this paper are in harmony with 
the views expressed in earlier papers as to the part played by the 
endodermis in the development of exudation pressures. 
16. Some of the consequences of applying these considerations 
to problems of physiological anatomy are indicated by a brief dis¬ 
cussion of the physiological relation of stelar strands to ground tissues 
in the Filicinese. 
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(1) Basecke, Paul. Beitrage zur Kenntnis der physiologischen Scheiden der 
Achsen und Wedel der Filicinen. Bot. Zeit. 66, p. 25. 1908. 
(2) Beckley, V. A. The Formation of Humus. Journ. Agric. Sci. 11 , pp. 66- 
77. 1921. 
(3) Bower, F. O. Presidential Address to Royal Society of Edinburgh, 1920. 
Proc. 41, p. 1. 1921. 
(4) Conrad, M. and Gutzheit. Uber die Entstehung und Zusammensetzung 
der Huminsubstanzen. Bey. dev Deutsch. Chew. Ges. 19, pp. 2844- 
2850. 1886. 
(5) Cranner, B. Hansteen. fiber das Verhalten der Kulturpflanzen zu den 
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wand lebender Zellen. Jahrb. fiir Wissensch. Bot. 53, pp. 536-598- 
1914. 
(6) - Beitrage zur Biochemie und Physiologie der Zellwand und der 
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