Hoagland —66— Plant Nutrition 



and his colleagues (1938), on the large marine coeno- 

 cytic alga Halicystis. An ingenious method had been 

 developed for inserting capillaiy tubes in these cells 

 in such a way that experimental solutions could be 

 introduced into the interior of the cell, to replace the 

 natural sap. Also bioelectric potentials across the 

 protoplasm could be measured by a similar technique. 

 So long as the cells remained healthy and had access 

 to an adequate supply of oxygen, a steady bioelectric 

 potential across the protoplasm was maintained. When 

 deprived of oxygen the potential fell greatly, some- 

 times near to zero, but was restored when oxygen was 

 again made available. This reversal could be repeated. 

 Moreover, the direct current resistance of the cells 

 was markedly increased under anaerobiosis. Numer- 

 ous measurements of the effects of modifying the 

 composition of the sea water medium on the bio- 

 electric potentials, with and without oxygen supplied, 

 were also carried out. The general interpretation of 

 all these experiments was that differential ion mobility 

 was immediately responsible for the bioelectric poten- 

 tials, although their ultimate source had to be sought 

 in metabolically released energy. The point of interest 

 now is that the cells were considered to become more 

 impermeable to salts in the absence of oxygen than 

 they were in its presence, until the anaerobic con- 

 dition resulted in irreversible changes in the cell, in 

 the direction of injury. 



COLLANDER (1939) from his experiments on large 

 algal cells living in brackish water came to the con- 

 clusion that exchange of cations between the vacuolar 

 sap and the outer medium was exceedingly slow — in 

 other words, that protoplasmic membranes were highly 

 impermeable to cations, at least. You will recall the 

 experiments on Nitella cells I described earlier in this 

 paper which showed that the cells were relativelyjm- 

 permeable with respect to the outward movement of 

 salt to distilled water. A similar result based on ex- 

 periments with roots was also noted. 



