Water Deficit or Unsatisfied Hydration Capacity. 93 



The main features of imbibition are determined by the carbohydrate- 

 protein ratio and the presence of salts. Animals and some vegetal 

 organisms are high in proteins. The vacuole and the external layer 

 of the protoplasmic units in plants give a play of osmotic activities 

 not duplicated in the animal ; and lastly, as has been so clearly estab- 

 lished by the work of Dr. H. A. Spoehr, the plant has a characteristic 

 carbohydrate metabolism with the capacity for the synthesis and com- 

 bination of the amino-acids, while in animal processes metabolism is 

 more largely concerned with the proteins, and amino-acids result 

 chiefly or entirely by disintegration of albumins. 



The ordinary conception of growth implying the changes in dimen- 

 sions of the developing parts of organs, shoots, roots, etc., is, however, 

 a well-rounded one of sound value and worthy of attention as a uni- 

 fied procedure. The ultimate physical forces concerned are those 

 which find play in elastic gels, and the interaction of these forces may 

 be modified by the self-altered composition of the living colloids and 

 by the action of external agencies under the influence of which these 

 colloids operate. 



The course of growth in the succulents will come hi for a large share 

 of attention hi the following chapters. The form of the organs of 

 such plants facilitates the making of observations in which the actual 

 temperature of the living mass may be found with some exactness, 

 and the large bulk which characterizes them makes it comparatively 

 easy to obtain analyses showing the varying proportions of the con- 

 stituents of importance in growth. Some attention has been given 

 to plants with thin stems and slender leaves, which in reality constitute 

 the dominant vegetative type of plants. 



The arrangement of imbibition tests of the growing terminal inter- 

 nodes of stems, and other organs, and the interpretation of the results 

 was made upon the basis of the supposition that such material was in 

 effect a complicated salted colloid, with an altering and unsatisfied 

 hydration capacity. The manner in which saturation might be 

 reached by immersion in various solutions might well offer some 

 profitable comparisons with the behavior of biocolloids of known 

 composition and structure. The earlier trials were made with the 

 growing parts of stems of Phytolacca decandra, Micrampelis calif ornica, 

 and Rudbeckia laciniata. The young internodes furnished sections 

 about 1 cm. long and of a thickness from 4 to 8 mm. A tangential 

 slice was cut from one side to remove a segment of the fibrovascular 

 tissue, and the plane surface exposed served to seat the sections firmly 

 in the glass testing-dishes of the auxographs. The first series was 

 made with distilled water, sodium or potassium hydroxide, and citric 

 and formic acids, all in hundredth-normal concentration. 



The series which were run in a day-lighted laboratory at tempera- 

 tures of 18 to 22 C. agreed in swelling most in distilled water, less in 



