84 Hydration and Growth. 



up of less than 3 per cent dry matter and more than 97 per cent 

 water, and hence approximated the dispersion of active protoplasm. 



Other sections from the same plate swelled 2,094 per cent in 18.5 

 hours at 16 to 18 C. The use of potassium nitrate and citric acid 

 (0.01 N) resulted in a shrinkage of less than a hundred per cent within 

 an hour, after which the volume was stationary. As the experiences 

 of the two sets of sections had been identical hitherto, it is interesting 

 to note that in this stage of imbibition (95 per cent water) acidified 

 salt produced more shrinkage than the salt alone, a result in harmony 

 with those obtained by swelling biocolloids. Imbibition in the salt 

 being generally greater than in the acidified salt, replacement of the 

 acidified salt with the alkaline salt was followed by a swelling amount- 

 ing to over 300 per cent of the original thickness of the sections in 9 

 hours, at the end of which time the swelling had not reached its limit. 

 Replacement with water speeded the imbibition to a rate which made 

 an increase of over 800 per cent in 9 hours. The sections now con- 

 tained nearly 97 per cent water, having swelled 3,156 per cent, and 

 when the water in the dish was replaced with acidified potassium 

 nitrate (0.01 M), the shrinkage was greater than in the previous experi- 

 ence, now amounting to 300 per cent of the original thickness of the 

 sections. A further shrinkage followed the substitution of alkaline 

 salt solution. 



Tests were arranged to ascertain the effect of the initial hydration 

 medium, using salts and acidified salts. Trios of sections of agar 90 

 parts and oat protein 10 parts, 0.18 mm. in thickness, were put under 

 the auxograph in a darkened chamber which remained steadily at 18 

 C. during the week in which the measurements were made. 



The sections which were immersed in hundredth-molar potassium 

 nitrate reached a size within 100 per cent of the possible total in 

 16.5 hours, at which time the expansion was about 1,200 per cent. 

 The replacement of the salt by distilled water which was renewed 

 twice induced an additional expansion of 1,750 per cent in 22.5 hours, 

 which was the practical limit of the sections. Replacement with 

 hundredth-normal acidified potassium nitrate resulted in a shrink- 

 age of about 100 per cent, the movement being complete in 6 hours. 

 Replacement of the acidified salt with water (renewed three times) 

 induced a slow, long-continued swelling, which, at the end of 18.5 hours, 

 had resulted in an increase of about 100 per cent, and which carried 

 the sections back to the maximum thickness attained before the acidi- 

 fied salt was added. The water was now replaced by a simple hun- 

 dredth-normal potassium-nitrate solution, which produced a shrinkage 

 slightly less than that displayed 24 hours before in acidified salt. This 

 was followed by a long-continued swelling, which again, in 21 hours, 

 brought the sections to the maximum thickness. The change to an 

 acidified salt solution resulted hi a shrinkage about equivalent to the 



