142 



Hydration and Growth. 



Mr. Long's results were confirmed by the author in April 1918, at 

 which time auxographic methods and technique of measuring the 

 swelling of such sections had been brought to an advanced stage of 

 eflBcacy. Sections were cut at sunrise, noon, and sunset, from young 

 joints 8 to 10 cm. long growing in the open under natural conditions. 

 Such sections had an average thickness of about 4 mm. and when 

 swelled at 20° C. gave the increases shown in table 108. 



Table 108. 



The great increase of dried sUces is indicative of high water capacity 

 of living material. The relative swelling of the sections in the different 

 solutions is identical with that of the fresh sections, demonstrating that 

 the dominant process is imbibition rather than osmosis. 



The time required for satisfaction varied widely with the time at 

 which material was taken and the character of the solution. The 

 sections taken at the end of the day were fully hydrated in distilled 

 water and began to shrink in 6 hours. The sections taken at sunrise, 

 which were most highly acid, as those taken in the evening are least 

 acidified, were satisfied in 2 hours and began to shrink in 3 hours. The 

 material taken in the morning was saturated in the acid solution in less 

 than an hour and was shrinking rapidly an hour and a half after 



8 a.m. 



8 a.m. 



Fig. 32. — The tracing on the left shows the variation in volume of a trio of sections of a young 

 joint of Opuntia 4.6 mm. in thickness which swelled 6.5 per cent in citric acid, 0.01 N, less 

 than three hours at 20° C, then began to shrink. The tracing on the right shows the 

 reaction of a similar trio which had an average thickness of but 3.9 mm., and which 

 swelled 6.4 per cent in an hour at 28° C. and then began to shrink very rapidly. 



immersion (see fig. 32). Swelling in the alkaUne solution was charac- 

 teristically slow and long-continued. Material taken in the morning 

 continued to increase for 4 hours, and that taken in the evening was 

 still showing some increase 12 hours later. 



Another feature in conformity with the condition of the joint at differ- 

 ent times of the day was the fact, confirmed by repeated tests, that the 



