2 5 



315 



E 

 o 



(M 



38 



E 

 o 



M 



20 



495 



E 

 o 



Figure 4. Cellular differentiation in median cross sections through 3 parts of barley roots 

 and the relative accumulation of bromide in them. Right: Anatomy of barley root ("low- 

 salt" type), at different distances from apex. Nos. 1-3, cortex and piliferous layer with- 

 out suberized exodermis. No. 4, 0.6 mm. from apex — differentiation of vascular strands 

 quite evident. No. 5, 5 mm. from root apex — unsuberized endodermis. No. 6, 1-3 cm. from 

 root apex — endodermis suberized but with passage cells opposite xylem groups. No. 7, 3- 

 5 cm. from root apex — endodermis suberized, without passage cells, and, at extremity of 

 segment, also thickened. Up, piliferous layer: E, endodermis; x, xylem; Ph, phloem; P, pas- 

 sage cells; C, central cavity (axile vessel). Left: Absorption of bromide by segments, ex- 

 pressed in m./e. per 1000 gm. fresh weight. External medium, 5 m./e. per L. of KBr. 



"Low-salt" roots (white area) from plants 9 days old, grown in distilled water; absorp- 

 tion period 24 hours. "High-salt" roots (blackened area) from plants 15 days old, grown in 

 nutrient solution; absorption period 23 hours. — Prevot and Steward (61 ) 



