MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 339 



The Behavior of Carbohydrates and Proteins in Gels Useful 

 IN the Interpretation of the Action of Plants. 



The amorphous carbohydrates constitute a very important part 

 of the colloids of the protoplast, the remainder of which consists 

 largely of nitrogenous material, in the form of albumen or albumen 

 derivatives with an unknown amount of lipin. The search for 

 material which might simulate the imbibitional behavior of growing 

 tracts in plants begun by the senior author resulted in finding that 

 mixtures of agar with gelatine in which the last-named substance 

 was present in the smaller proportion showed an enhanced capacity 

 for imbibition in distilled water and a reduced swelling in weak acid 

 and alkali as measured in very thin plates by the auxograph.^* 



The swelling of gelatine in percentages of the original thickness 

 of thin dried layers or plates (.i to .3 mm. in thickness) in water, 

 hydrochloric acid and sodium hydrate, may be illustrated by the 

 following data which represent averages of measurement at the 



Fig. 9. Auxographic tracing of swelling of agar sections .2 mm. in thick- 

 ness in NaOH N/100, A =400 per cent., in HCl N/100, B — 650 per cent, 

 and in distilled water, C = 775 per cent. X lO- 



end of sixteen hours (see p. 343 for further discussion of swelling 

 determinations by use of thin plates). 



Water. 



471.S per cent. 



HCl N/ioo. 



1012.3 per cent. 



NaO N/100. 



587.S per cent. 



Similar plates of agar gave swellings as follows (Fig. 9) : 



Water. 



462.5 per cent. 



HCl N/100. 



725 per cent. 



NaO N/ioo. 



937.5 per cent. 



1* MacDougal, " Imbibitional Swelling of Plants and Colloidal Mixtures," 

 Science, N. S., Vol. 44, No. 1136, pp. 502-505, October 6, 1916. See also Ann. 

 Report, Dept. Bot. Res., Carnegie Institution of Washington for 1916, pp. 61-64. 



