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(Read April 21, 1921.)

The suggestion was made in an earlier paper that the common metals which enter into nutrient solutions might find their chief importance in restricting, limiting or defining hydration of the cellcolloids.1 MacDougal and Spoehr carried out a series of tests upon this matter and found in fact that the strong metallic bases when used at concentrations of 0.01 N do limit or restrict the hydration of agar according to their place in the electromotive series, the least swelling taking place under the action of the strongest base, with rubidium unplaced. Beginning with the strongest the series runs K(Rb) NaLi, and if calcium were added to the series the swelling under its action was less than that in potassium.2

When the concentrations were reduced however to 0.001 N it was found that hydroxides of all of the metals increased the hydration capacity of agar. This was of importance as a review of all of the available data seems to show that the range of the H+-OH- balance in the plant cell lies between the values expressed by Pнз and PH II, or between about 0.01 M aspartic, succinic or propionic acid and under 0.001 N KOH.

The reversal of effects at great attenuations in the hydroxides led to the extension of auxographic measurements upon the effects of low concentrations of the salts which are of such interest and importance in cultures, and the action of chlorides, nitrates and sulfates of potassium, calcium, sodium and magnesium upon agar, gelatine and mixtures was made at Carmel in the summer of 1920. 1 MacDougal, D. T., “Growth in Organisms," Science, 49: 599-605, 1919. (See page 11 of reprint.)

2 MacDougal, D. T., and H. A. Spoehr, "The Components and Colloidal Behavior of Plant Protoplasm," Proc. Amer. Phil. Soc., 59: 154, No. 1, 1920.

PROC. AMER. PHIL. SOC., VOL. LX, B, JULY 25, 1921.

A preliminary announcement of the fact that excessive hydration values in agar and biocolloids were obtained when these substances were swelled in dilute salt solutions was made before the Physiological Section of the Botanical Society of America at Chicago, December 28, 1920, which is in press in the American Journal of Botany for June, 1921. Also of interest in this connection is the announcement of Loeb of the reversals of specific effects of salts above and below M/16 on the swelling, osmotic pressure, and viscosity of gelatine.3

S. C. J. Jochems measured the effects of a number of acids, bases and salts upon stems of Laminaria, Fucus, agar, carrageen and upon a number of seeds in 1919. The wealth of results include a number of important generalizations as to the behavior of the plant mucilages and organs when swelled in a number of solutions with a wide range of concentrations.

Jochems found that no rule could be formulated for the influence of the basicity of the acid radicals in the swelling of agar and that the effect of the valency of the base was very small. Still more surprising is the conclusion reached by Jochems that while nearly all of the salts tested, NaCl, NaBr, NaI, NaNo,, Na,So,, Na2HPO,, CaCl2, lessened swelling at 0.01 M, at 0.05 M the imbibition was greater than in water. The agar was commercial material and some of the differences between these conclusions and the facts discussed in the present paper are to be attributed in part to my use of a specially purified agar.*

My own experiments were planned to test the action of salts of interest in connection with nutritive solutions within the range of biological interest, which would lie between 0.01 M and 0.0001 M. Single series of swellings in KOH and HCl were included for purposes of comparison.

The first series of tests were made with two plates of agar a year old. Plate A swelled 1,800 per cent. in thickness and 3 to 4 per cent. in length when freshly made, and Plate B, 3,000 per cent. in

3 Loeb, J., "The Action of Salts in Low Concentration," Jour. Gen. Physiol., 3: 391-414, 1921.

Jochems, S. C. J., "De imbibite van plantaardige celwanden in oplossingen van electrolyten." Published by A. H. Kruyt, Amsterdam, 1919. See pages 35-46.

thickness and 3 per cent. in length. Increases in thickness and volume of sections of the two plates at 14-15° C. are given below. The agar used was of a specially purified lot which had been freed from salts and diffusible carbohydrates by dialysis, and a thin solution was sprayed into 10 times its volume of neutral acetone. The resulting fine shreds were subsequently extracted with hot absolute acetone, absolute alcohol and absolute ether.

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-1,630 1,800

Th. Vol. Th. Vol.

- 2,260 2,540

1,140 1,305 1,420 1,565 1,570 1,730 2,500 2,800 1,720 2,000 2,400 2,645
|1,000 1,145 1,160 1,325 1,355 1,520 2,300 2,680 1,750 2,040 2,700 2,975
750 824 750 824 1,100 1,340 1,470 1,590 1,630 1,925 2,100 2,315
640 705
725 830 900 945 1,100 1,190 1,500 1,751 1,950 2,160

The accelerating effect of the potassium hydroxide in its weakest, and its retarding effect at its strongest concentrations, confirms previous results by Spoehr and MacDougal. This maximum effect is in a 0.001 M solution with a PH value of II. A lesser swelling takes place in either a weaker or a stronger solution.

If we now pass to the acid reactions it will be seen that in HCI at 0.001 N with a PH value of 3 the swelling of the agar is little short of that in water. At some point between this concentration and. 0.0001 N swelling becomes equivalent to that which might take place in water and at the last named concentration with a PH value of 4.2 the hydration is much in excess of that in water, being as 128 with that in water taken as 100.

The purified agar used has a PH value of 6.5 when made up at 0.75 per cent., which is near the limit of its gelation at 15° C. in the 5 MacDougal, D. T., and H. A. Spoehr, "Hydration Effects of Aminocompounds," Proc. Soc. Exp. Biol. and Med., 17: 33-36, 1919. "The Components and Colloidal Behavior of Plant Protoplasm," Proc. Amer. Phil. Soc., 59, No. 1, 150, 1920. Swelling of Agar in Solutions of Amino Acids and Related Compounds," Bot. Gaz., 70: 268–278, 1920.

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