THE IMBIBITIONAL SWELLING OF MARINE ALGAE 



J. M. McGEE 



University of California, Berkeley, California 



The data obtained by MacDougal as to the swelling of biocol- 

 loids composed of agar as a basic carbohydrate and of varying 

 proportions of different nitrogenous substances afford a basis for 

 the interpretation of the general constitution of plant tissues.' 

 This was borne out by the results of some swelling tests of marine 

 algae made at the Coastal Laboratory, Carmel, California in 

 July and August, 1917. The results include other points of 

 interest as described below. 



Iridaea laminarioides, Gigartina exasperata, and G. mammil- 

 losa var. dissecta, red algae growing on the rocks near Carmel, 

 were chosen for the tests. These plants have a sap balanced to 

 the imbibition and osmotic pressure of sea-water containing about 

 3.5% total salts, and the effect of various substances was ob- 

 tained by adding them to sea water in which sections were to 

 be immersed. Measurements were made by the use of Mac- 

 Dougal's precision auxograph (s6e table 1). 



The imbibition of Iridaea laminarioides indicates a high propor- 

 tion of amino-acids, as shown by the greater swelling in the acidi- 

 fied solutions. Gigartina, however, gives measurements indica- 

 tive of the presence of an agar-like substance, in greatest pro- 

 portion in mature fronds. This diagnosis is supported by the 

 results of swelling dried material. 



Smooth young laminae of Gigartina exasperata were washed 



^ MacDougal, D. T., Imbibitional swelling of plants and colloidal mixtures. 

 Science 44: 502-505, 1916. The effect of acids and salts on the swelling of 

 biocolloids. Science 46: 269-272, 1917. 



MacDougal and Spoehr, The behavior of certain gels useful in the interpreta- 

 tion of the action of plants. Science. 45 : 484-488, 1917. Growth and imbibition. 

 Proc. Amer. Phil. Soc. 56: 289-.352, 1917. See also reports of the Department of 

 Bot. Research, Carnegie Inst, of Wash, for 1916 and 1917. 



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