564 RADIATION BIOLOGY 



sea water was also studied in daylight and darkness. After exit had 

 started, it was found to be greater in light than in darkness. 



Ingold (1936), who made similar experiments with Elodea, found that 

 light increased the absorption of salts by the shoots immersed in water. 

 He referred to Hoagland's afore-mentioned hypothesis for an explanation 

 of his findings. 



If the interpretation of the results obtained by Jacques ct al. is correct, 

 the effect of light on the intake of substances would, in these instances, 

 be indirect only. The experiments would then rightly belong in the 

 category first mentioned in the present survey (see section on Indirect 

 Influences). 



Arisz (1947) studied the intake of salts — particularly of chlorides — by 

 leaves of Vallisneria. Because the wounds of the cut leaves influenced 

 the intake, the leaves were pretreated in distilled water for 24 hr. After 

 that time the influence of the wounds had subsided to a great extent. 

 As a result, it was found that the absorption of chlorine from a balanced 

 solution of potassium chloride and calcium sulfate depended on the con- 

 centration of chlorine in the external fluid, on the pH of the solution — 

 pH 4.5-9 being detrimental — and on the light. Exposure to light had a 

 remarkable effect on the strength of the absorption. The stronger it was, 

 the stronger the absorption. Light did not influence the intake by photo- 

 synthetic processes, since it was also active when carbonic acid was lack- 

 ing from the medium. Arisz referred to the investigations of Hoagland 

 and coworkers (Hoagland and Davis, 1923; Hoagland et al., 1926), 

 Jacques and Osterhout (1934), and Ingold (1936) and their conclusions 

 regarding the connection between photosynthesis and the influence of 

 light on permeability. Because Arisz 's experiments with Vallisneria 

 showed that light had the same influence in a medium free from carbonic 

 acid — i.e., without photosynthesis — their conclusions cannot be accepted 

 in the case of this plant. 



PhilHs and Mason (1937) found that cotton leaves absorbed sugar from 

 a sugar solution and formed starch only in the light and when supplied 

 with oxygen. This process also took place in a medium free from carbonic 

 acid. 



Collander (1939) investigated the effect of light on the intake of cations 

 in Chara ceratophylla and Tolypellopsis stelligera. Parallel tests were 

 made with plants both in diffuse daylight and in darkness in salt solu- 

 tions of approximately the same concentration as in the natural state. 

 After a few days the cell sap of the internodal cells was tapped off and 

 analyzed. The experiments showed that absorption — at any rate, of 

 lithium, potassium, rubidium, and strontium — was stimulated by light. 

 This influence was considerably stronger in the case of lithium than in 

 that of rubidium. It was also stronger in the case of Tolypellopsis than 

 in that of Chara. The amount of lithium taken up by Tolypellopsis in 



