106 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



added to one of sea-water shrinkage takes place in seven 

 hours, and increases in rapidity if the proportion of fresh 

 water be further augmented. This change in permeability 

 has been quantitatively studied by an electrical method to 

 be described later. 



Osterhout points out that the observed shrinkage in 

 volume of the protoplasm itself when transferred from sea 

 to fresh water directly negatives the theories of those 

 biologists who seek to explain effects, usually attributed 

 to osmotic pressure, as being due to imbibition or to the 

 giving up of water by the protoplasm. 



THE PERMEABILITY OF PROTOPLASM TO SALTS 

 AND IONS. 



Though salt solutions, when sufficiently concentrated, 

 bring about plasmolysis readily, yet it is not correct to 

 suppose that the protoplasm forms an impenetrable ob- 

 stacle to the entrance of the solute. The passage of sodium 

 chloride into leaves was demonstrated by the work of 

 Lewis described previously. Quantitative researches by 

 the author (1909) on the absorption of water by the seeds 

 of Phaseolus vulgaris showed that Jiving dry seeds took 

 up as much water from a decinormal solution of sodium 

 chloride as did those which had been killed by chloroform 

 vapour. There was no concentration of the solute in the 

 surrounding liquid, which shows that it penetrated in the 

 same proportions as did the solvent. 



Among the most complete studies upon the penetration 

 of salts into protoplasm must be considered those of Rufz 

 de Lavison (1911). This investigator studied their entry 

 into the central cylinder of roots through the protoplasm 

 of the cells of the endodermis and found that with weak 

 concentrations the kations of salts of the alkalies and 

 alkaline earths, united to non- toxic anions, penetrated the 



