Physiological Studies in Plant Anatomy 131 
For the present we may summarise as follows our conclusions 
with regard to the suberin lamella characteristic of the secondary 
stage of the endodermis. The lamella has a basis, differing from the 
basal substance of the Casparian strip in its ready solubility in 
sulphuric acid; it may possibly be a more resistant cellulose de¬ 
rivative chemically allied to the substances present in the thickening 
lamellae of the tertiary stage. This basal substance is impregnated 
with derivatives of suberogenic acids forming a product like suberin, 
but differing from typical suberin in that phellonic acid cannot be 
identified amongst the constituent acids. 
(2) The Undulation of the Casparian Strip. 
This phenomenon, frequently discussed by earlier observers, has 
been re-investigated during the micro-chemical study of the strips 
of Potamogeion endodermis. Schwendener ( 27 ) regarded the undulation 
as due to the disturbing effect of section-cutting upon the turgid 
tissues of the root. The cellulose walls being elastic contracted when 
the tension was released, whilst the Casparian strip, unable to con¬ 
tract, was thrown into folds. Van Wisselingh ( 32 ) agreed that in some 
cases the undulations first appeared in the section but pointed out 
that in other cases they could be seen in the living root. Like 
Strasburger( 28 ) he regarded the undulations as due to more rapid 
local growth of the wall during suberisation. Rimbach( 25 ) confirmed 
Van Wisselingh’s observation that the undulations are present in the 
living uncut root. He also showed that they may be produced (i) by 
plasmolysing the living endodermal cells with the aid of salt solutions ; 
on again transferring the tissues to water, the strips straightened out 
as the cells became turgid; (ii) as a result of the general contraction 
of the root after it had reached its maximum length in growth. In 
this case the undulations would occur in the suberised layers of the 
secondary or tertiary stage of the endodermis. 
In our observations upon the endodermal strips of Potamogeton 
it was always found that the walls of the cells of the endodermal 
cylinder, after maceration in water, were quite straight whether in 
the primary, secondary, or tertiary stage, but the Casparian strip 
could be thrown into the very characteristic folds by treatment either 
with potash or sulphuric acid. 
The employment of these strips made it readily possible to 
ascertain whether the formation of these folds was connected with 
cell contraction or expansion. In some cases the strips were placed 
on microscope slides over glass scales ruled in millimetres, in other 
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