80 Hydration and Growth. 



were again used at D and a slow shrinkage again set in which fol- 

 lowed on during the 18 hours until the change was made at E to 

 hydroxid, which, as before, simply neutralized the acid and increased 

 the salt-content, with the result that the volume of the colloid swelled 

 to the dimensions occupied before the last treatment with acid. At 

 the end of the 5 hours, F, the hydroxid was removed and water, re- 

 newed once, poured into the dishes. The effect was very marked, 

 as a rapid swelling ensued during the next 4 hours, at the end 

 of which time it was in progress at an undiminished rate, being greatest 

 in the formic and least in the citric acid. The sections now contained 

 a large proportion of water, sufficient to bring them into the condition 

 of hydration of active protoplasm, and the addition of the acids at G 

 arrested the swelling abruptly and caused a shrinkage which was di- 

 minishing at the end of 4 hours. The shrinkage was checked by replace- 

 ment with water at H and a slight swelling took place in the ensuing 

 11 hours. 



The water now being replaced by hydroxid, a sudden slight ex- 

 pansion occurred in all of the sections, followed by a shrinkage which 

 had not ceased entirely at the end of 9 hours, during which period 

 additional salts were being formed in the colloidal structure. Now, 

 when the hydroxid was partially washed out by water at J, a swelling 

 ensued which in 15 hours brought the sections very nearly to their 

 final thickness and consequently near their maximum imbibition 

 capacity. It is in this condition, of course, that growing protoplasts 

 are normally active. The greatest expansion in this phase was in the 

 material treated previously with malic acid. 



The addition of hydroxid (K) was now followed by a marked 

 shrinkage which had not ceased at the end of 8 hours. Replace- 

 ment of the hydroxid with acid at L caused a further abrupt 

 retraction which soon ceased, and after 5 hours the acid was re- 

 placed with water once renewed (M), only a slight swelling resulting 

 during the next 10 hours. Again hydroxid (N) caused a sudden 

 expansion to be followed by a slow shrinkage which had not reached 

 its end in 13 hours. Water now following hydroxid at 0, a much 

 greater expansion took place than when water followed acid. Alka- 

 losis at P now came after an hydroxid-water period and was not 

 followed by the abrupt enlargement consequent upon adding hy- 

 droxid to the colloid after an acid-water period. The shrinkage, 

 however, was as marked as in previous experiences, and had not ended 

 in 8 hours. 



Replacement with water at S was followed by an expansion which 

 had not ceased at the end of 6 hours. Finally, acids caused a diminu- 

 tion the most marked of any produced by these substances. Both 

 acids and hydroxids caused the most marked changes ni the highly 

 hydrated and salted sections near the end of the week over which the 



