Physiological Studies in Plant Anatomy 215 
At first chloroform was added to the salt solution to kill the root 
tips, but was extraordinarily slow in action and experience showed 
that the fall of resistance in the presence of chloroform was little 
faster than in the normal salt solution alone, as this also proved 
very toxic. The normal salt solution was then replaced by a 
balanced salt solution of suitable concentration, the optimal salt 
solution as ascertained by Shive( 25 ) being employed. Whilst in 
normal salt solution the resistance fell to a few hundred ohms within 
the first six hours, in this balanced culture solution the resistance 
remained steady for twenty-four hours, or even increased in amount. 
Having thus seen that the resistance of the living root remained 
steadily high, a drop of concentrated sulphuric acid was added with 
the result that the resistance fell within half an hour in a typical 
experiment from 7300 ohms to 700 ohms. With chloroform the same 
effect would be produced in the course of a few hours. Similarly, 
comparison was made between the resistance of a bean root before 
and after the meristematic tip was cut away. In this case, also, 
the removal of the tip was followed by a great increase in the con¬ 
ductivity of the root. 
These experiments, then, provide strong evidence that the 
healthy meristematic tissues are only penetrated with great diffi¬ 
culty if at all by the ions carrying the electric current. In all cases 
a considerable proportion of this small current that passes will be 
carried by the surface films around the tissues, so that the actual 
amount of penetration of the meristematic tissue by the solute 
present must be very small indeed. 
The three lines of experimental evidence thus briefly summarised 
are concordant in supporting the conclusion that the meristematic 
tissue at the root apex is relatively resistant to the passage of both 
water and solutes. 
II. A Comparison of the Water Relations of Root 
and Stem Apices 
(1) The Relations of a meristematic tissue to Water 
The following theoretical considerations are now advanced in 
further support of the experimental evidence that the tissue, closing 
the endodermis at the root apex, is under normal conditions imper¬ 
meable to water. 
The cytology of any meristem always reveals certain charac¬ 
teristic features. The cells in the apical meristem of the root, for 
instance, are filled with protoplasm, non-vacuolated and closely 
