50 CARNEGIE INSTITUTION OF WASHINGTON. 



ance of the course of slow enlargement was noticeable in the records. At 

 concentrations of 0.03M to 0.04M, however, a slight retardation lasting for 

 an hour or more was noticeable. At concentrations of 0.05M for KCl, 

 NaCl, and CaCl2 a slight but positive contraction ensued. This did not 

 take place in sea-water until a concentration of 0.06M for the contained Na 

 was reached. After contraction for an hour or two expansion was resumed, 

 as shown in figure 1. The consequent increase could not be determined 

 with sufficient exactness to be of value. 



The solutions given above, which produce a contraction of the sections, 

 may be taken to be slightly hypertonic to the cells; that they are not 

 isosmotic is obvious; that the contraction of the cells due to increased permea- 

 bility and loss of water, is brought about by the colloidal action of the 

 various salts seems plain. 



The aggregating or combining effect of the salts becomes even more obvious 

 when the effects of the higher concentrations are considered. Sections in 

 concentrations above CaCU, 0.07M lost the power of expansion, while this 

 did not occur with Na until a concentration of 0. 14M was reached, sea- water 

 at 0.16M, and with K until a concentration of 0.18M. It may be safely 

 assumed that these concentrations serve to rend the plasmatic layer from the 

 wall in an irreversible plasmolysis. 



This effect is evidently not one of tonicity, as the isosmotic values of 

 critical solutions which produce an irreversible contraction are widely apart. 

 The concentrations, however, do form a series expressing the relative penetra- 

 bility or permeability of the kations concerned. The aggregating effect 

 which would produce a permanent lessening of permeability is designated by 

 the concentrations given, and the three bases form the series Ca, Na, and K. 



Fig. 1. — Facsimile of auxographic records of living sections of Opuntia which were first hydrated 

 in water at 16° to 19° C. for 6 to 9 hours, then placed in solutions of sea-water. When the 

 concentration reaches 0.06M a slight contraction followed by expansion takes place. At 

 concentrations above 0.16M plasmolysis ensues and the contraction is permanent. The por- 

 tion of the record in which contraction is in progress is reproduced by a dotted line. 



Relative Effects of Some Common Ions on Hydration, Absorption, and Per- 

 meability, by D. T. MacDougal. 



That the action of the common salts of the soil on plants is in the main 

 determined by the ionic mobility of the particles, with modifications due to 

 the varying composition of the living material and with interferences, is 

 suggested by the following data taken from recently published papers and 

 from manuscripts now in preparation : 



Total swelling of dried sections of Opuntia. 



Auxographic measurements, in percentages of original thickness: 



KCI, 310 Sea-water, 310; NaCl, 280; CaCU. 275 at O.OIM; water 255: 



Time necessary for satisfaction of living sections of Opuntia in salt solutions at O.OIM.: 

 KCl, 30 NaCl, 28; CaCla, 36 hours. 



