LABORATORY FOR PLANT PHYSIOLOGY. 49 



study is certainly suggestive and, while these results are in no sense final, 

 they indicate some of the lines of investigation which may be followed in 

 attempting to explain diverse behavior of plant cells toward salt solutions. 



Relative Effects of Common Metals in producing Contraction, Expansion, and 

 Plasmolysis of Cell-Masses, by D. T. MacDougal. 



The cell-sap of vacuolar contents, in addition to sugars, contains amino- 

 acids and salts of the common bases, including nitrates, sulphates, and 

 chlorides. When cells with such contents are placed in distilled water, the 

 deficit, which may almost invariably be recognized, is taken up by the en- 

 trance of water with a consequent increase in volume. If, now, salts be 

 added to the water in a similar experiment, the permeability of the wall will 

 be affected by the action of these salts in forming compounds with the material 

 in the layers of cell material, the solution out of some of the material, and 

 the colloidal action of the kations and anions on the colloidal aggregates of 

 the wall and plasma. The result may be an increase or a contraction of the 

 cell, according to conditions. The diffusion of the ions into the cell will be 

 mainly determined by their ionic mobility, which in the common bases will 

 be as K 64.7, Na 43.6, Ca 51.8. Their action in aggregating effects will be 

 in proportion to the residual charges they carry, which will be in the above 

 order, but with the least effect by potassium and the greatest by calcium. 



Now, when cell-masses which have been fully hydrated in water are placed 

 in a salt solution which is isotonic or slightly hypertonic to the cell-sap, it is 

 found that a contraction ensues which continues for a short time, after which 

 expansion takes place, which does not, however, carry the cell to the volume 

 which it had when fully hydrated in distilled water. The proportion of the 

 contraction which is regained is taken by Kahho to indicate the degree of 

 change which has been produced in the permeability of the cell. Thus NaCl 

 at 0.0141M gave a resumption of 29 to 30 per cent, at 0.181M gave 35 to 54 

 per cent, while roots in CaCl2 at 0.134M showed no return toward the original 

 dimensions. These solutions being isotonic, Kahho concludes that the 

 penetrability of the potassium is greatest, but that the permeability is 

 lessened most by the calcium, with the action of the sodium lying between. 



It was important that these tests should be repeated with other material. 

 Joints of Opuntia were chosen for this purpose. Living sections of this 

 material, which were in a condition in which they would swell 150 to 160 per 

 cent in thickness in pure water, were placed under the auxograph in water, 

 and after 6 to 9 hours, when the increases amounted to 120 to 130 per cent, 

 the water in the immersion dishes was replaced with graduated series of 

 potassium, sodium, and calcium chlorides. 



This method of auxographic measurement not only enables the observer 

 to see the exact thickness of the sections at any moment, but he has also a 

 visible record of the changes from the beginning, and with the ten instru- 

 ments available it was possible to carry a large number of tests through 

 simultaneously at the identical temperatures, which thus did not need to be 

 kept constant or under uniform illumination. The immersion liquids in the 

 tests below varied from 16° to 20° C. 



The plan implied that a series of sections was first hydrated in water to 

 the extent indicated, then the water was replaced by salt solutions, begin- 

 ning with those in 0.01 M concentration. At this concentration no disturb- 



