278 BOTANICAL GAZETTE [October 





agar plate were allowed to swell by alternating every 12 hours 

 water and ammonium hydroxide in 0.01N solution. The curve 

 for this swelling is reproduced in fig. 5. At first both the XH 4 OH 

 and the water cause swelling. As the hydration continues, however, 

 the swelling in NH 4 OH becomes slight, and finally there is an 

 actual shrinkage in the hydroxide with, moreover, a subsequent 

 swelling again in the water. The total swelling thus attained 

 greatly exceeds that in water or ammonium hydroxide alone. The 

 total swelling of the dried agar plates treated thus alternately 

 with water and ammonium hydroxide was 5300 per cent, or on the 

 basis of the swelling in water equal to 100, the swelling in alternating 

 NH 4 OH and H 2 equaled 134. Similar experiments were carried 

 out in which glycocoll was alternated with water. Thus with 

 18 changes in 15 days agar swelled 191 as against 100 in water. 

 In a solution of glycocoll which was not changed during the entire 

 swelling the agar showed a swelling value of 132. The curves thus 

 formed by the swelling of agar in glycocoll are shown in fig. 6. 



No adequate explanation has been found for the augmenting 

 effect on the. swelling of agar produced by ammonia and the amino 

 acids and here described. From a consideration of the relative 

 effects of various hydroxides it would appear that something 

 analogous to salt formation and subsequent hydrolysis of this 

 compound may be involved. 4 Ammonium, as a weak base united 

 with agar, an exceedingly weak acid, would form a salt which would 

 very easily be hydrolyzed. * Under conditions in which this hydrol- 

 ysis is suppressed by the presence of a common ion (NH 4 ), the 

 excessive swelling does not take place. Thus when dried agar 

 plates are allowed to swell by alternating solutions of 0.001N, 

 NH 4 OH, and NH 4 C1 the total swelling does not exceed that 

 attained in water, but actually falls somewhat below that value. 



The possible biological significance of these changes in volume, 

 which are also exhibited by agar-protein mixtures with respect to 

 growth and metabolism, seems to be so great as to warrant, not 

 only this brief description, but also the formation of plans for the 

 extension of the experiments. 



Desert Laboratory 

 Tucson, Ariz. 



4 Bracewell, R. S., Jour. Amer. Chem. Soc. 41:1511-1515. 1919. 



A. 



