62 



CARNEGIE INSTITUTION OF WASHINGTON. 



Such a mixture is seen to swell most in distilled water, while the pro- 

 portionate swelling in alkali is very high, being greater than that in 

 the salts tested or in acid. Next, it is apparent that the two potassium 

 salts produce or allow an amount of imbibition not very much short 

 of that in the alkaU. The acidification of the salts practically reduces 

 the swelling to the proportion displayed by the acid alone. 



It appeared to be important to form a series in which the sweUing 

 in alkaline salts would be included. The first measurements were 

 made with dried plates a week old of agar 90 parts, nucleinic acid 10 

 parts, 0.2 mm. in thickness. The sweUings were as follows: 



The effects of a similar series of reagents were tried upon disks from 

 growing joints of Opuntia with the following results: 



Distilled water 



Potassium nitrate, 0.01 M 



Potassium nitrate-citric acid, 0.01 M 



Citric acid, 0.01 M 



Potassimn nitrate-potassium hydrate, 0.01 M 



P. ct. 



10.8 

 8.7 

 9.8 

 9.2 



10.4 



The differences are not very great, yet it is to be noted that they 

 are in the same direction as those of the biocolloid (agar-nucleinic acid). 

 The imbibition is greatest in distilled water, scarcely less in alkaUne 

 potassium nitrate, and definitely less in acids and neutral salts. All 

 of the above tests were made at temperatures of 15° C. to 18° C. 



The data cited above serve to show some of the more obvious features 

 of imbibition in a biocolloid as affected by conditions similar to those 

 supposedly prevalent in living plants. 



