TRUE & HARVEY: ABSORPTION OF CALCIUM SALTS 503 



maintained at i8° C. by automatic control so accurate that the range 

 of variation was seldom above four tenths of a degree Centigrade 

 during the course of an experiment running a fortnight. The con- 

 tainers remained in darkness except during the short time required 

 for the determination of the conductivity which took place in rather 

 faint diffused light. Since it is obviously unsafe to draw conclusions 

 from a comparison of ohms, results were always calculated to concen- 

 trations expressed as gram-normals of the salt in question dissolved 

 in a million liters of water (grm. norm. X io~^). The water was 

 obtained by twice distilling Potomac River water from glass with 

 electric heat in a laboratory from which gas was excluded. Each 

 experiment was usually continued until signs of deterioration began to 

 appear in the seedlings. 



Calcium Nitrate 



Several experiments were carried out with squash seedlings in 

 calcium nitrate solutions. Since they were in close agreement but 

 one is preseoted here, that running from May first to May fifteenth, 

 last, inclusive. The distilled water used in making up the solutions 

 had an initial conductivity equal to that of a solution containing 11.7 

 grm. norm. X lO"^ Ca(N03)2- Nine cultures each containing 5 seed- 

 lings and 500 cc. of solution were set up in a series ranging in con- 

 centration from 18.2 to 867.0 grm. norm. X lO"^. Daily observations 

 were made until signs of exhaustion began to appear. Since in the 

 cultures containing less than 50 grm. norm, the behavior of the seed- 

 lings varied so little in the different members of the series only a part 

 of the record is shown here in order not to confuse the table with 

 several nearly coinciding curves. In the curve representing the 

 record of the culture in distilled water a dashed line is employed 

 (Fig. i). 



It will be observed that in both distilled water and in cultures 

 containing calcium nitrate up to a concentration of 100 grm. norm. 

 X io~^ the solutions gain in concentration for two or three days, a 

 course which in the distilled water is followed by a very slight ab- 

 sorption until near the close of the experimental period. At no time, 

 however, were the plants able to regain any considerable proportion 

 of the electrolytes lost to the medium during the first few days. 



With the dilute solutions of the salt (under 100 grm. norm.) this 

 period of leach gradually passes over into one of active absorption 

 as a result of which these solutions are reduced to a lower ion content 

 than the distilled water. 



As the initial salt content of the solution is increased to approxi- 

 mately 500 grm. norm, the slight leach seen in the weaker solutions 



