Physiological Studies in Plant Anatomy 227 
through the meristematic tissue. Furthermore, the experiments by 
Miss Helen Heaps in this laboratory already referred to (p. 213) 
supply decisive evidence in the case of iron salts, that the salt never 
enters the living root through the apical meristem but can be traced 
Water 
Cork 
Plasticine 
Gelatine 
by appropriate methods, diffusing into the cellulose walls in the 
absorptive region of the root until held up at the Casparian strip 
of the endodermis, then diffusing across the endodermal barrier 
through the protoplast. 
Summary 
1. Recent work upon the sap pressures existing within the 
vascular strand leads to the conclusion that the meristematic cap, 
closing the endodermal cylinder in the young root, must be relatively 
impermeable to water. 
2. It is shown experimentally that this meristematic cap will 
prevent the passage of water under a pressure of two atmospheres. 
3. This meristematic tissue is relatively impermeable to the 
diffusion of salts in solution and acid dyes but stains very readily 
with basic dyes. 
