212 J. H. Priestley and R. M. Tupper-Carey 
therefore allowed to grow into short lengths of tapering glass 
tubing. After a day or two the roots had become firmly fixed into 
the tubes with the apex protruding beyond the narrow end. The 
roots were then cut off, with the glass tube attached, and watertight 
connections obtained by wiring the pressure tubing on to the wide 
end of the glass tube. The other end of the pressure tubing was 
connected to the short arm of a long J-shaped glass tube, by means 
of which water could be forced into the root with the aid of a 
column of mercury in the long arm of the tube. A T-join closed 
by clip or tap, between the short arm of the J and the pressure 
tubing attached to the root, permitted the removal of air bubbles 
that otherwise might have accumulated against the cut surface of 
the root. 
When eosin solution was driven into the root under a pressure 
of one atmosphere no leakage took place at the root apex, not even 
when the apex was chloroformed and left attached to the apparatus 
all night. A fine glass capillary was then driven into the root far 
enough to penetrate the endodermal cylinder, whereupon the eosin 
solution mounted rapidly in it. When sections were cut off this root 
the cells of the meristematic cap were only faintly stained although 
the dye had stained the other tissues deeply, including the cortex 
(see p. 213). Similarly, no leakage of a solution of malachite green 
took place when forced into the roots under a pressure of about two 
atmospheres, until again the endodermis was pierced by a fine capil¬ 
lary tube. The growing point also remained completely unstained, 
although it is shown later that the meristematic cells stain rapidly 
with such basic dyes when they come in contact with them. In this 
case, no movement of the sap in the vascular strand being possible, 
the basic dye did not reach the meristem within the period of experi¬ 
ment (from one hour to twenty-four hours on different occasions). 
Experiments on these lines, then, have confirmed the earlier 
experimental results of de Vries ( 28 ) and drawn attention to the fact 
that the apical meristem as well as the endodermal cylinder con¬ 
tributes to retain the sap when under pressure. 
(2) Experiments with Dyes and Salts in Solution 
Many observations have been made upon the entry into the 
root of dyes and various inorganic salts and these experiments lend 
considerable support to the view that the meristematic tissues are 
impermeable to most solutes though they stain extremely readily 
with basic dyes, in high, probably toxic, concentration. Acid dyes 
