September 14, 1917] 



SCIENCE 



269 



the spread of cotton rust in the Eio Grande 

 valley of Texas. J. J. Taubenhaus 



Division of Plant Pathology 

 AND Physiology, 

 Texas Agricultural Exp. Station, 

 College Station, Texas 



SPECIAL ARTICLES 



THE EFFECTS OF ACIDS AND SALTS 

 ON "BIO-COLLOIDS" 



Mixtures of agar with gelatine, albumen, 

 protein, vxea or amino-acids in which the 

 agar forms seventy-five per cent, or more of 

 the whole, show a similarity of imbibitional 

 behavior to that of sections of plants and 

 hence for convenience in the present studies 

 may be termed " hio-colloids." The results 

 of a series of tests with a wide variety of 

 nitrogeiious substances from urea to albumen 

 were in general agreement to the effect that 

 such substances mixed in proportions of one 

 to ten, more or less, with agar, when made 

 into thin dried plates, swelled enormously; 

 2,000 to 3,000 per cent, in distilled water, one 

 half to one tenth this amount in hundredth- 

 molar hydrochloric acid, and more or less in 

 hundredth-molar sodium hydrate.'^ 



An extension of the tests of the effects of 

 nitrogenous substances upon the swelling of 

 the amorphous carbohydrates was made to 

 include a mixture of agar and peptone the 

 swelling measurements of which were as fol- 

 lows : 



AGAR 90 ^PEPTONE 10 



Water HCl ifllOO NaOH .U/lOO 



3166.6% 500% (20 hours) 633% 



, 566.6 (20 hours) 800 



633.3 (48 hours) 1,666.6 



The chief feature of interest in these 

 results is the uniform swelling in alkali in 

 excess of that in hydrochloric acid, in a man- 

 ner slightly different to that of similar mix- 

 tures in which other nitrogenous substances 

 were used. 



1 See ' ' Growth and Imbibition ' ' presented be- 

 fore the American Philosophical Society, April, 

 1917, and now in press in the Transactions of the 

 society ; also ' ' The Behavior of Certain Gels Useful 

 in the Interpretation of the Action of Plants," 

 Science, 43, p. 484, 1917. 



The chief purpose of the entire series of 

 studies has been to ascertain what conditions 

 of growth and development might be iden- 

 tical with the factors affecting imbibition. The 

 fact that plant protoplasts usually consist of a 

 large proportion of carbohydrate gels with a 

 smaller proportion of nitrogenous material 

 has already been discussed. The resulting 

 colloidal mixture may be acidified as a result 

 of certain respiratory processes, or this acid 

 may be broken up as fast as formed, in which 

 case the protoplast might be in a deacidified 

 or neutral condition and from this might vary 

 to alkaline under conditions which we are not 

 yet ready to describe. Acidification and de- 

 acidification of the cell may take place at a 

 rapid rate and be complete within a short 

 time, according to the bulk of the cell-mass, 

 temperature and other conditions. 



Hydrochloric acid had been used in nearly 

 all of the earlier work for acidification of 

 colloids, since most of the knovra. facts as to 

 the swelling of gels are referable to it. The 

 acids of the plant are organic, and a mod- 

 ification of the technique to heighten the 

 similarity between the experiments and the 

 action of the plant was to substitute citric 

 for hydrochloric acid in the series. 



Preliminary to this substitution, series of 

 swellings were carried out to test the relative 

 action of the two acids, with the following 

 results from dried plates of mixtures of 90 

 parts agar and 10 parts bean protein: 



Hydrochloric Acid Citric Acid 



jV/IOO -V/100 



541.6% 916.6% 



875 

 875 



300 402 



916.6% 



The effect of this organic acid in this initial 

 series of tests was to produce an imbibitional 

 swelling fairly equivalent to that of sodium 

 hydrate and to cause such colloidal mixtures 

 to take up more water than in hydrochloric 

 acid. An extended series of measurements 

 will be necessary before any serious conclu- 

 sion can be formulated, however. 



Another set of factors arising from the 

 presence and concentration of salts is next to 



