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CARNEGIE INSTITUTION OF WASHINGTON. 



The outstanding fact that a mixture consisting mostly of gelatine 

 to which a small proportion of agar has been added shows its greatest 

 swelling in alkaline solutions is the most important feature of these 

 results. The mixture in question is available as a physical analogue 

 which has already been found useful in the study of growth and swelling 

 of plants. Mixtures consisting half or more of gelatine give acid 

 swellings of second rank and expand least in water. Mixtures contain- 

 ing more than half of agar swell most in water, with the effects of 

 weak acids and alkalies fairly equivalent. 



dwelling of agar-geluline 7nixturcs. 



The results described constitute a gratifying success in the search 

 for a colloidal mixture which would exhibit the swelling reactions of 

 plant-cells. The variations in imbibition exhibited by these mixtures 

 are of a kind and range displayed by the plant, and it seems probable 

 that the addition of a hexose albumen and of minute quantities of 

 salts would make a still more accurate analogue of the plant. Both 

 agar and gelatine are colloids of the emulsoid type believed to be 

 composed of two aqueous phases differing from each other only in the 

 relative concentration of the organic compound in the water. The 

 behavior of agar-gelatine mixtures is therefore of much interest in 

 connection with prevalent theories of the structure of gels of this type, 

 as well as with relation to the nature and behavior of the plant colloids. 



Causes of Variations in the Transpiring Power of Cacti, by Edith B. Shreve. 



During the assembly of the data secured from the investigation of 

 the transpiration of cacti, which has been under way for the past two 

 years, it became evident that further experimentation was advisable. 

 Measurements of transpiration, of water-intake by the roots, of water- 

 absorbing capacity of the tissues, of relative acidity of the tissues, and 

 of stomatal movement have now been made under various controlled 

 environmental conditions. These experiments have shown the exist- 

 ence of a constant interrelation between transpiring power and water- 

 holding capacity of tissues, water-content of the aerial parts of the 



