90 



Hydration and Growth. 



These elementary experiments open a field of possibilities as to the 

 incorporation of new material in masses of swelling colloids, in exempli- 

 fication of some phases of cell-mechanics, inclusive of the action of 

 embryonic cells in growing regions. The author, in collaboration with 

 Spoehr and Richards, has recently been able to outline the manner 

 in which the xerophilous and the succulent types of shoots or organs 

 are due to the action of such superposed effects in the cell colloids. 

 A series of detailed analyses of the carbohydrate-content of the opun- 

 tias, which was arranged to determine the principal sugars not only 

 during developmental stages, but also to follow the changes through- 

 out the seasons, established the fact that when these plants were sub- 

 subjected to long periods of drought, resulting in partial desiccation, 

 polysaccharids were dehydrated, with the result that the sugars, which 

 have a low water capacity, became converted into pentosans or muci- 

 lages, which have a large imbibition capacity. This fact was amply 

 confirmed by the coefficients of swelling which were obtained in my 

 own tests, which ran through several years. 



Following this, the fortunate discovery was made that Castilleia 

 latifolia, which is native to the region about the Coastal Laboratory, 

 has thin, highly acid leaves when growing under mesophytic conditions, 

 but has less-acid succulent leaves in arid locations, the increased size 

 of the leaves being due to the hypertrophy of the thin-walled paren- 

 chymatous tissues. The hydration reactions of the two types of 

 leaves in a fresh and dried condition are shown in table 70, which gives 

 the swellings in 0.01 normal citric acid at 15 C. 



TABLE 70. 



In the interpretation of these results, it is to be noted that drying, 

 both from the fresh state and from the hydrated condition, reduces the 

 hydration capacity of the thin leaves, but not of the succulent ones. 

 The principal changes in hydration include the extraction of acids and 

 salts as well as the hexoses, while the mucilaginous pentosans diffuse 



