120 



Hydration and Growth. 



This fact suggests that the general optima of the plants grown at the 

 different temperatures differ in such manner that the one grown at the 

 higher temperature has the lower optimum, and conversely, that the 

 one grown in the cool chamber has its optimum at a higher temperature, 

 which is not necessarily at the point at which the tests were made. 

 The exceptions in the last case in the alkaUne solutions may afford a 

 clue to the actual physical conditions upon which such differential 



Table 97. 



Opuntia etiolated at 

 17° to 19° C. 



Swelled at 

 17° to 16° C. 



Swelled at 

 30° to 31° C. 



Opuntia etiolated at 

 30° to 31° C. 



Swelled at 

 17° to 19° C. 



Swelled at 

 30° to 31° C. 



Distilled water 



Potassium nitrate 



Potassium nitrate, citric acid, 0.01 N 



Citric acid, 0.01 N 



Potassium nitrate, potassium hy- 



droxid, 0.01 M 



Potassium hydroxid, 0.01 N 



p. ct. 

 4.2 

 4.8 

 4.9 

 3.2 



13.7 

 10.6 



hrs. 



16 



30 



3 



3 



36 

 36 



p. ct. 

 7.5 

 6.5 

 9.5 

 4 



9.5 



8 



hrs. 

 1.5 

 6 

 1 

 1 



1.3 



p. ct. 



13.2 



12.7 



7.3 



4.4 



hrs. 



40 



48 



4 



4 



p. ct. 

 3.7 

 7.3 

 3.7 

 3.3 



hrs. 

 8 

 8 

 1 

 1 



action rests. According to Jenny Hempel, the hydrogen-ion concen- 

 tration of etiolated lupine shoots was not much different from that of 

 normal green plants, although the actual quantity of acid was much 

 greater. The amount of acid in the plant grown at the higher temper- 

 ature would, in accordance with general experience, be less than in 

 those grown at the lower temperature.^ The only suggestions available 

 for an explanation of the behavior in question would rest upon the as- 

 sumption that the amount of acid was the critical feature, and also 

 that the plants grown at higher temperature had experienced the con- 

 version of the polysaccharids into the pentosans, which have a rela- 

 tively high coefficient for swelling (see p. 91). 



It is to be noted, in any consideration of the action of the colloidal 

 systems, that fresh or living sections of plants are already in the con- 

 dition of the colloidal sections which have been immersed 4 to 8 hours, 

 and that it is the behavior of the sections after they have taken up 

 90 per cent of their total capacity for water which comes into the 

 realm of the living plant. Dried sections of plants come down to a 

 water-content not much above that of colloids. It also is to be remem- 

 bered that in the advanced stages of the desiccation of cell-masses the 

 protoplasmic coUoids are subjected to the action of the dissolved elec- 

 trolytes in a concentrated condition in the final stages of drying. The 

 fixation of the salts and acids which takes place under these circum- 



1 Hempel, J. Buffer processes in the metabolism of succulent plants. Compt. Rend. d. Trav. d. 

 Lab. d Carlsberg, 13: No. 1. 1917. 



