II. FUNDAMENTAL FEATURES OF PHYTOCOLLOIDS. 



It became evident in the earlier stages of the studies described in the 

 present work that the swelling of gelatine does not afford a parallelism 

 to the action of vegetative cell-masses of the higher plants, and that 

 only in certain reproductive elements or in some of the lower forms is 

 the proportion of nitrogenous material sufficiently great to give reac- 

 tions similar to those of gelatine. Experimental demonstrations of the 

 general character of the cell colloids was first made with sections of 

 joints of Opuntia. The results of an extended series of analyses of 

 these plants made by Dr. H. A. Spoehr covering all of the seasonal 

 changes were available, and from his results it can be seen that their 

 general composition is about as shown in table 1.^ 



Table 1. 



The hydration of an organ or cell-mass with a composition similar 

 to that shown in table 1 would of course be determined by the hydro- 

 lyzable carbohydrates and proteins and affected by the salts. 



The first experiments were directed to ascertaining some of the 

 reactions of the carbohydrates which are known chiefly or entirely in 

 the colloidal form and which might be a constituent of the plasmatic 

 gels. The most readily available representative of these substances 

 was agar. Strands of the material were liquefied in water at 60° or 

 70° C, poured into shallow molds with the area of a postal card, and 

 allowed to desiccate to plates from which pieces 3 by 5 mm. were cut. 

 Swelling was measured by the auxograph, using an improved form, the 

 essential part of which consists of a compound lever, the members of 

 which are pivoted in adjustable bearings in a rigid brass frame.^ The 

 bearing lever has a forked free end suitable for the attachment of a 

 counterpoise and of a vertical swinging arm of twisted brass wire. 

 The free portion of this vertical lever is sheathed with a section of 



^MacDougal and Spoehr. Growth and imbibition. Proc. Amer. Phil. Soc, 56 : 335. 1917. 

 Philadelphia. 

 *76id., 327. 



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