VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 557 



his observations into accord with Heilbrunn's calcium-release theory 

 (1937). According to this theory, the stimulating agents — among them 

 light — cause a breakdown in a cortical calcium-containing gel, with the 

 resultant passage of free calcium ions to the cell interior. It causes a 

 brief transitory liquefaction at this site, soon followed by gelation or 

 clotting of the protoplasm. Alsup stated that calcium must be associ- 

 ated with the influence of light but that experimental results do not 

 otherwise substantiate the theory. 



INFLUENCE OF VISIBLE LIGHT ON PERMEABILITY OF CELLS 



INDIRECT INFLUENCES 



The relation between light and permeability is complicated, particu- 

 larly in the higher plants, by the fact that the exchange of water and 

 solutes in cells and organs is dependent on the physiological state of other 

 parts of the same plant and on the physiological processes taking place 

 there. Light may exert either an indirect influence on the exchange of 

 substances by affecting such states and processes or a more direct influ- 

 ence by affecting the permeability of the cells. This twofold effect con- 

 stitutes an unfavorable factor for the analysis of the influence of light 

 on the permeability. Because both modes of action are intermingled 

 physiologically, it is often difficult to determine which one causes an 

 observed alteration in the light-induced exchange of substances. 



That indirect effects occur has been shown by the following experiments: 

 Schmidt (1936) found that illumination of the aerial parts of higher 

 plants changed the salt intake of the roots growing in the dark. As a 

 test object he used Sanchezia nobilis, which he grew in a nutrient solution. 

 Since the intake of ions is dependent on, among other factors, the (juanti- 

 tative intake of water, the experiments were arranged in such a way that 

 the water metabolism of the plants was uniform. Illumination (2500 

 m-c) of the aerial shoots was accompanied by an increase in the intake 

 of potassium, magnesium, and the nitrate ion and a decrease in the 

 intake of calcium and phosphate by the roots growing in the dark. The 

 effects varied with the strength of illumination. With an increase in 

 the intensity of illumination of the shoots, there was an increase in the 

 intake of potassium and magnesium by the roots. A maximum was 

 reached at approximately 2500 m-c and remained constant with an 

 increase in the strength of illumination. Conversely, a decrease occurred 

 in the intake of nitrate, phosphate, and calcium, a minimum being reached 

 at approximately 900-1000 m-c. The intake subsequently rose with the 

 increase in the strength of illumination. Within the minimum range the 

 roots gave off calcium and phosphate to the surrounding solution. The 

 salt intake of the roots was also found to be dependent on the pretreat- 

 ment of the shoot with hght or darkness. 



