

SWELLING OF AGAR IN SOLUTIONS OF AMINO 



ACIDS AND RELATED COMPOUNDS 



D. T. MacDougal and H. A. Spoehr 



(with SIX figures) 



i 



A study of the behavior of a large Variety of substances in 

 aqueous solution on the hydration of agar has shown that there 

 are very few such solutions in which agar swells to a greater degree 

 than it does in distilled water. There are some substances, how- 

 ever, which increase the hydration of agar above that attained in 



1 MacDougal, D. T., Auxographic measurement of swelling of biocolloids and 



of plants. Box. Gaz. 70: 126-136. 1920 



Botanical Gazette, vol. 70] 



[268 









pure water. These are the amino acids. The amino compounds 

 are of such immediate biological importance that a discussion of 



* 



their action deserves special consideration, and may aid in explain- 

 ing the scattered results obtained by various workers in which 

 increased total growth and apparently catalytically accelerated 

 actions have been obtained by the addition of certain amino acids 

 to culture solutions. 



The purification of the agar, as well as the preparation of the 

 agar plates and the instruments and methods for measuring the 

 swelling, have already been described in detail by MacDougal. 1 

 The results here discussed were obtained by the application of J 



these methods. The amount of swelling in water is taken as the 

 standard. Thus the percentage of swelling of the dried plates in 

 water is expressed as 100, and that in the various solutions is 

 calculated on this basis. 



Swelling of agar in solutions of amino acids 



The dried agar plate, prepared from the specially purified 

 agar and used in this experiment, showed a total swelling in dis- 

 tilled water of 2000 per cent. The amino acids, glycocoll, alanin, 

 and phenylalanin were used in 0.01 normal concentration. The 

 solutions in which the agar plates were allowed to swell were 

 renewed every 24 hours; the swellings were complete after about 

 6 days. The results are given in table I. 





