MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 293 



alkaline media or distilled water was much greater in the young joints. Of 

 interest is the observation that the colloidal material from mature joints 

 which have been freed as much as possible from the fibro-vascular strands 

 showed a diminution in volume in weak alkaline solution. 



Mr. E. R. Long also working at the Desert Laboratory made 

 some tests of this matter and found that the swelling capacity of 

 sections of Opuntia discata as determined by weighing, was less in 

 acidified than in neutral solutions and that the swelling was some- 

 times less in alkaline solutions than in distilled water.^ These results 

 suggested that it would not longer be profitable to consider the 

 plant as a protein gel and that some comprehensive tests would 

 be necessary to establish the general colloidal character of growing 

 parts. 



This mistake had been made by Borowikow* who assumed that 

 plant cells would grow in an acid condition like a mass of gelatine, 

 showing the greatest imbibition of water in acids. 



The action of plant tissues having been determined, it was 

 attempted to make up mixtures of colloids similar to those occur- 

 ring in the plant which might show parallel reactions. The tech- 

 nique and results of measurements of the swelling of plant tissues 

 and of plates of colloidal mixtures will be given in a separate section 

 of this paper. It may be said in this place that some highly profit- 

 able comparisons are made possible by the data obtained. 



The effort to compound colloidal mixtures which might simulate 

 living material was extended to include additions of other proteins 

 beside gelatine, such as egg-albumin, bean-albumin and of amino- 

 acids, together with complex condensed carbohydrates as agar. 

 This was rewarded by results which show that small proportions of 

 soluble proteins or albumens added to gelatine-agar mixtures 

 decrease the water-absorbing capacity of these physical analogues 

 of the protoplasts in the presence of electrolytes, and suggest the 

 highly interesting possibility that the growth-enlargement of the 

 cell might be definitely checked or terminated by the passage of such 

 albuminous emulsions from the nucleus to the cytoplasm. The 



3 " Growth and Colloid Hydratation in Cacti," Botan. Gazette, 59: 491, 

 1914. 



* Biochem. Ztschrft., 48: 230-246 and 50: 1 19-128, 1913. 



