T. C. Br oyer 241 



distinctly different types of tissue external and internal thereto may 

 not be without merit (2/). Conditions within the cortex and its relative 

 volume certainly favor high levels of accumulation as well as a large 

 quantitative proportion of inorganic solute therein (6/). 



2 3 4 5 

 DISTANCE FROM 



6 7 8 9 



APEX IN CM. 



Figure 25. The gas exchange of successive segments of ex- 

 cised barley roots. Measurements made on 72 segments in 2 

 ml. of dilute nutrient solution; temperature 24 ° C; ex- 

 perimental time, 2 hours. — Machlis ($0) 



The longitudinal pattern of inorganic solute distribution in roots has 

 been observed by several investigators. One of the first experiments, 

 under controlled conditions of short time study, was that by Prevot and 

 Steward (6/) using abscised roots. They showed that inorganic solute 



