108 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



to such experiments the objection has been raised that the 

 permeability of the protoplasm had been thereby altered, 

 and that it was not shown by subsequent observation that 

 the cells remained uninjured. Osterhout (1913, 1) in- 

 vestigated the absorption of calcium salts by growing 

 roots in distilled water, whereby the root-hairs were ob- 

 tained free from crystals. On being placed in tap-water 

 or dilute solutions of calcium salts, the appearance of 

 crystals of the oxalate could soon be observed, thus proving 

 the penetration of the calcium salts. These cells con- 

 tinued to develop in a normal manner. The absorption of 

 oxygen and excretion of carbon dioxide by plant cells shows 

 that the protoplasm is permeable to these substances. 



PRECAUTIONS NECESSARY IN PLASMOLYTIC 

 INVESTIGATIONS . 



In order to guard against errors in the plasmolytic 

 method, previously overlooked, attention was directed by 

 Osterhout (1913, 1) to the following points: 



1. The necessity of finding a solution which could be 

 used as a standard in comparative studies. The chief 

 requirement of such a medium is that it should have a 

 purely osmotic action, involving no alteration of the normal 

 permeability of the plasmatic membrane. Quantitative 

 measurements by the electrical method showed that re- 

 agents such as solutions of sucrose, sodium chloride, or 

 potassium nitrate, were not without an injurious action, 

 though previously considered to be quite free from ob- 

 jection on this score. It was shown, however, that sea- 

 water fulfilled the requirements of such a solution, for in it 

 the various salts are present in such proportions that their 

 toxic effects mutually balance each other. Accordingly 

 sea-water, suitably concentrated or diluted, was taken as 

 the standard medium for investigations upon plasmolysis. 



