Constituents of Biocolloids Affecting Hydration and Growth. 31 



it impossible to secure measurements by the methods which may be 

 used with agar and with gelatine. Information as to their effects can 

 only be obtained by observations on the action of mixtures of which 

 they form a part. Table 11 includes some of the data as to the swell- 

 ing of colloids, including pentosans secured in this laboratory. 



It is also obvious that the addition of any of these gums or mucilages 

 to agar tends to lessen swelling in water and to equalize the imbibition 

 in water and in acids. Their general effect, however, when combined 

 with nitrogenous substances, is to make a colloid which has a higher 

 coefficient of swelling in water than in organic acids, although, as may 

 be seen later, a special relation is sustained to the amino-acids. 



The vacuolar fluid of the plant cell probably always contains some 

 protein or its derivatives in the form of amino-acids, while various 

 nitrogenous compounds have been identified in the nucleus and other 

 bodies of morphological rank. The formation, disintegration, and 

 migration of these substances from one part of the cell to another 

 offers a most inviting field for the researcher concerned with the physics 

 of the cell. 



The proteinaceous substances are of course invariable constituents 

 of the biocolloids of the plant protoplast. The varying reactions of 

 such material to the hydrogen-ion concentration or acidity of solu- 

 tions and to salts are exemplified in nearly every section of this work. 

 Combinations of agar with protein extracts, with albumins, peptones, 

 gelatine, and amino-acids were tested to such an extent that it is 

 possible to say that the highest coefficients of hydration in water alone 

 are exhibited by pentosan-albumin mixtures in which the substances 

 of the first group form the greater part of the mixture. All such trials 

 were with materials with possible physiological significance, especially 

 in plants. 



Many of the nitrogenous compounds used in making biocolloids in 

 our tests are known to be actually present in the cell. The presence 

 of one of them, peptone, in the nucleus is definitely established. A 

 characteristic behavior of the mixtures containing such substances has 

 already been noted (see MacDougal and Spoehr, The effects of acids 

 and salts on biocolloids, Science, 46: 269. 1917). Increases of nearly 

 3,200 per cent in distilled water, 567 per cent in hundredth-molar 

 hydrochloric acid, and the superior and long-continued swelling in 

 hundredth-molar potassium hydroxid, which sometimes reached a 

 total of nearly 1,700 per cent at room temperatures (20 to 28 C.), were 

 the characteristic features. These figures were obtained by the use of 

 sections consisting of 90 parts agar and 10 parts Witte's peptone. 



The tests were repeated, using "Diffco" peptone in the same pro- 

 portion and with temperature kept strictly at 15,C., and the records 

 given below are all at the close of 22 hours. The measurements were 

 as follows: 



