Physiological Studies in Plant Anatomy 115 
Efforts in this direction have so far met with no success, presum¬ 
ably because the endodermal tissues are so much more exposed to 
the action of the macerating agent under these conditions that their 
disintegration is as rapid as that of the xylem strand within. 
Complete success was however obtained by other means. Leafy 
stems of Potamogeton perfoliatus L., in which the endodermis is 
strongly developed and the xylem absent, were collected in great 
quantity. The plant stalks, freed from leaves, are placed under damp 
cloths and left for some days to decompose. They are then immersed 
in water, and with a little practice it is easy to extract from the partly 
rotted material the central endodermal cylinder, still quite firm and 
unaltered; light rubbing between finger and thumb removes the 
slight traces of cuticle remaining at the nodes. If the material is 
subsequently dropped into concentrated sulphuric acid, the residue 
is certainly more than 99 per cent, pure endodermal tissue, less 
hydrolysable cellulose. This tissue forms a very delicate cylinder; so 
long as it is in concentrated sulphuric acid its texture is so mucilaginous 
and fragile that it is difficult to handle, but when the acid is diluted 
to about 10 per cent, the cylinders become of much firmer con¬ 
sistency. They then float at the surface of the liquid and can easily 
be picked up with a bent platinum wire. They are then washed free 
from sulphuric acid and dried; and in this state provide material 
suitable for macro-chemical investigation. 
By this means, during 1920, some 2-3 gms. of relatively pure 
endodermis were collected and some useful preliminary chemical data 
obtained. The further macro-chemical investigation is being pursued 
but will be a slow process because of the scale upon which opera¬ 
tions have to be carried out to obtain enough of the material for 
analysis. In the meantime, this method of isolating endodermal 
tissue has provided material, in the shape of endodermal strips 
isolated from the rotting material, which has been of very great value 
for the micro-chemical studies. These strips, if allowed to rot further 
in water, remain coherent endodermal cylinders from the centre of 
which the parenchymatous tissue altogether disappears. Material 
prepared in this way has been widely employed and frequent reference 
is made to it subsequently under the term of endodermal "strips.” 
Unfortunately the method is not readily applicable to all plants 
even for micro-chemical purposes where complete removal of the 
xylem is not necessary, and although the endodermis of other plants 
has been studied in this way, productive results have been obtained 
mainly from Potamogeton. 
8—3 
