Physiological Studies in Plant Anatomy 213 
will not stain living roots after many days immersion. This is very 
strikingly shown by roots, of cuttings (Salix and Tradescantia were 
used), which have been grown continuously in water. These roots 
will continue to grow in o-i per cent, solution of acid dyes such as 
acid green, and the new apical growth appears completely un¬ 
stained. On the other hand, many experiments referred to elsewhere 
(Priestley (20)) have shown that many such dyes penetrate the cor¬ 
tical tissues of the root behind the growing point, diffusing through 
the walls of the cells until stopped by the impermeable walls of 
exodermis or endodermis. 
In experiments with electrolytes in which the distribution of the 
kations can be subsequently examined by characteristic colour re¬ 
action, no cases have been noted where the kations could be detected 
in the meristematic cells, except on occasion where toxic effects had 
clearly preceded or accompanied their entry. Thus in healthy 
willow roots (Salixfragilis L.), the distribution of potassium followed 
by MacallunTs(i6) sodium cobalt-nitrite reaction, and in bean and 
pea roots the distribution of iron taken up from 1/40,000 N ferrous 
sulphate, showed a sharp restriction to the vacuolated region behind 
the meristematic apex. Iron salts in more concentrated solution 
frequently proved toxic and then the iron could be detected within 
the meristematic tissue, but so long as the roots remained healthy 
and capable of growth iron salts could not be detected within these 
cells by any reaction either for free or combined iron (Macallum ( 15 ); 
Jones ( 9 ^). This statement is supported by a long series of observa¬ 
tions made in this laboratory by Miss Helen Heaps, M.Sc., in an 
investigation of the path followed by iron after its entry into the 
root. These observations then suggest that though the protoplasts of 
the root meristem readily take up the colour group of a basic dye, 
inorganic salts and dyes in solution cannot penetrate this tissue so 
long as it is alive. 
(3) Conductivity Experiments 
The high resistance shown by this apical root meristem to the 
passage of an electric current, suggests that electrolytes are unable 
to move freely through it. The resistance was experimentally deter¬ 
mined with the aid of the apparatus shown in text-figure 1. The 
bean root was mounted upon a platinum wire with which contact 
was made through a mercury lead enclosed in a sealed bent glass 
tube. The bean root was immersed in a paraffin-vaseline mixture 
of low melting point so that it could be poured into the vessel at 
