62 Hydration and Growth. 



Trios of sections of agar swelled 1,875 per cent in a 0.01 N solution of 

 acetic acid at 18° C, while a combined solution of equivalent molecular 

 concentration showed a swelUng of 1,750 per cent. 



There now remained the test with Uving tissues. Some joints of 

 Opuntia blakeana of 1918, which had been brought from Tucson two 

 months earlier and had laid on the table, with the result that they had 

 lost much water but were still alive, were used for this test. A trio of 

 sections with an average thickness of 6 nun. swelled 60 per cent in the 

 hundredth-normal acetic acid, while a similar trio which measured 

 5.5 mm. on the average swelled but 45.5 per cent in the combined 

 acetic-glycocoU solution. A second feature distinguished the two 

 reactions, the swelling in the acetic acid being continuous and ap- 

 proaching zero during the 20 hours of measurement, while in the com- 

 bined solution full expansion was reached in 4 hours, after which a 

 shrinkage rfesulted in a loss of nearly 5 per cent, suggesting that the 

 H-ion concentration of the combined solution was greater than that 

 of the acid alone. 



A return was made to the biocoUoidal mixtures and trios of sections 

 of agar 8 parts and oat protein 2 parts, with a thickness of 0.22 mm., 

 swelled at 18° C. The hydration in the hundredth-normal acetic acid 

 gave an increase of 1,318 per cent, while an equimolecular solution of 

 the acetic acid and glycocoU gave a swelhng of 1,605 per cent. This 

 test is the only one of the series in which the addition of glycocoll to 

 the acetic acid enhances imbibition. In this last test the amount of 

 solution poiu-ed in each dish was such that the same quantity of the 

 acetic acid was present in both. 



An additional test was made in which equal amounts of glycocoll and 

 acetic acid were brought together at a concentration of 0.001 M each 

 on agar-oat protein sections as above. The swelling in the acetic 

 acid was 2,681 per cent, or about the same of that possible in distilled 

 water (2,630 per cent), while the swelling in the combined solution was 

 shghtly less, being 2,570 per cent. 



Glycocoll and other ancdno-groups are present in the plant in com- 

 paratively great dilutions, and probably at no time does the amount 

 present reach the concentration in which a retardation or limiting of 

 the hydration effect would be exerted. The experiments described 

 show that glycocoll and asparagin may actually increase the hydration 

 capacity of pentosan and of pentosan-protein colloids. The meager 

 results obtained from swelling plant-sections are not harmonious and 

 further experimentation is highly desirable. The accelerating effect 

 of glycocoll is a subject which has come up for notice many times. 

 Dakin connected its action with possible catalytic effects.^ The simi- 

 larity of the results obtained from agar and agar-protein mixtures 



'^ Dakin, H. D. The catalytic action of anaino-acids, etc., in effecting certain syntheses. Joui. 

 Biol. Chem., 7: 49-55. 1909. 



