424 Martin : Effect of concentrated solutions 



that urea and glycerine readily penetrate the protoplast without 

 injury. Klebs ( lo, page 540) states that glycerine not only pene- 

 trates the protoplast, but is there metamorphosed, and as shown 

 by Meyer (14^) and Laurent maybe converted into starch by cer- 

 tain higher plants ; but, he continues, that the presence of glycer- 

 ine in the cell-sap does not increase the turgor, since water-extrac- 

 tion by potassium nitrate took place normally. 



Other experiments do not seem to bear out this view. De 

 Vries found that the osmotic pressure was increased by urea (33^) 

 and glycerine (33^) so that a much stronger concentration of other 

 plasmolyzing solutions was required to induce plasmolysis again. 

 Famintzin's experiments (7) with the culture of algae showed that 

 by a gradual increase in the concentration of the medium a very 

 considerable number of salts could be transferred into the cell-sap, 

 and the cells in this way accustomed to stronger solutions. 



The experiments in the present investigation showed, in nearly 

 every case, an increase in the concentration of the cell-sap under 

 the influence of glycerine, urea, and acetamid. Of the plants used 

 in the experiments, Tradescantia showed the least concentration in 

 cell-sap, and the least increase in concentration. Yet in some 

 cases glycerine doubled the concentration of the sap, and the 

 action in general w^as much stronger than w^ith urea or acetamid. 

 Urea increased the concentration in Tradescantia much less than 

 in the other plants studied. 



Relation between increase of concentration of sap ^ and concentra- 

 tion of solution, — There is considerable difference in the action of 

 these substances. Although the final concentrations often do not 

 show great differences, if these concentrations are compared with 

 the original concentrations of the plasmolyzing substances, the 

 greater increase in osmotic pressure due to glycerine will be 

 brought out. The results with red beet cells may be cited as an 

 example. The plasmolyzing concentration of glycerine was 2///3> 

 that of urea 3^/2 which gives a difference of 5;//6. Yet the same 

 or a less concentration of potassium nitrate was required to re- 

 plasmolyze cells treated with these solutions, showing that gly^^^" 

 ine was able to produce a comparatively greater osmotic pressure 

 than urea. 



This difference is much more marked in the case of acetamid. 



