Robert B. Whhrow 



393 



PERMEABILITY 



It has been known for many years that light in the visible and near- 

 ultraviolet regions of the spectrum directly alters the capacity of many 

 plant tissues to take up inorganic salts and organic solutes through 

 processes other than those involving transpiration. Likewise, the ca- 

 pacity to retain these solutes against osmotic gradients is influenced. 

 Lepeschkin (29, jo) found that certain dyes are accumulated more 

 rapidly in Elodea in light of relatively high intensities than in dark- 



TABLE II 



Influence of Transpiration on Absorption of Salt by Barley Plants of Low-Salt, 

 High-Sugar, or High-Salt, Low-Sugar Status (from T. C. Broyer and D. R. 



Hoagland) 



Experimental Conditions 



Water 



Ab- 

 sorbed, 

 ml./g. 

 fresh wt. 



Shoot 



Salt Absorbed 



in m.e. X io"/g. 



total fresh wt. 



(loss from 



culture) 



K Br 



Total Sugar, 



g./b 



Shoot Root 



High salt; low humidity, light 8.10 5.20 6 



High salt; high humidity, light 2.58 3- 2 4 4 



High salt; high humidity, dark 1.49 1.59 2 



Low salt; low humidity, light 9.60 10.85 9 



Low salt; high humidity, light 3. 60 10.40 9 



Low salt; high humidity, dark 2 . 52 8 . 75 9 



07 



2 4 

 15 

 5 2 

 65 

 *3 



5 4 

 2.9 



°-3 



15 3 



6.2 



2.0 



1 . 1 

 0.7 



trace 



3-5 



2-5 



0.8 



ness. He concluded that the protoplasmic permeability was increased 

 and that the most effective spectral region was in the blue and near- 

 ultraviolet range from 320 to 420 mu. Similar results were obtained by 

 Oflford and d'Urbal (42) with Nitella. Jacques (2j) observed that the 

 uptake of ammonium ions from sea water as well as the exosmosis of 

 ammonium ions to ammonium-free sea water is higher in Valonia 

 plants exposed to daylight than those kept in the dark. On the other 

 hand, Zycha (60) and Jacques and Osterhout (24) have found that the 

 accumulation of potassium in Nitella was relatively independent of 

 radiation. 



