SALT RELATIONS OF VASCULAR PLANTS 



113 



I50r 



40 



- 30 



20 



12 3 4 5 6 7 8 



Distance from root tip, mm 



o 

 o 



c E 



O 1- 



-150 



- 40 



- 30 



60 



50 40 30 



Distance from root tip, 



20 



10 



■D 



e 



E 



20 



mm 



10 



Branch roots Xylem completely Root hairs 



formed differentiated formed 



Protoxylem 



differentiating 

 Fig. 38. Zones of salt absorption and accumulation in roots 

 a. Radioactivity of various regions of living barley roots after immersion in 

 rubidium phosphate containing *®Rb and ^^P, for 3 hr at 25 °C. The dotted 

 line indicated radioactivity in a comparable volume of medium. (Redrawn 

 from Overstreet and Jacobson, 1946); b. Respiration rate (O O), accumula- 

 tion of ^^P (C O), and translocation of ^^P (O — O) in different zones 



of barley roots (redrawn from Kramer, 1956). 



In more recent experiments using a similar technique, Van den 

 Honert et al. (1955) observed no significant effects of transpiration 

 rate on absorption of ammonium, potassium, nitrate and phosphate 

 ions by Zea mays. Broyer and Hoagland (1943) showed that 



