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ILLINOIS ACADEMY OF SCIENCE 



If in the frame-work and cell wall systems of plants in gen- 

 eral such a simple structure is primary, there must also exist 

 a secondary and grosser structure which determines the aniso- 

 trophy as manifested in unequal swelling along the several axes 

 due to water absorption. Wood, for instance, swells most 

 tangentially, less radially and least longitudinally, while a great 

 variety of unequal swelling appears in wall structures show- 

 ing hygroscopic movements. In some of these cases only a 

 single wall is involved, showing anisotrophy to exist in rather 

 minute structures whether primary or secondary. The multi- 

 vacuolate conception of gel structure lends itself more readily 

 to the explanation of this anisotrophy, for with water gain 

 and loss the vacuoles may show greater dilation and contrac- 

 tion in certain axes than in others (7: pp. 745-552). 



The thing of greatest biological interest in the study of hy- 

 drosols and hydrogels, including the protoplasm, is not any 

 specific structure found, but the capacity for the assumption 

 of one or another structure with variation in condition. The 

 reaction is now reversible and now! irreversible. While such 

 modifications are brought about with relative ease in gels and 

 sols in vitro, it seems that living protoplasm and its constitu- 

 ents are even more labile. This is illustrated by Lepeschkin's 

 (8a) work showing that slight pressure will cause a reversi- 

 ble flocculation of cell proteins of Spirogyra and greater pres- 

 sure, a permanent coagulation and death. Pressure alone does 

 not coagulate protein in vitro. According to Lepeschkin some 

 of the proteins of plant cells essentials to life would coagulate 

 in a few hours, or at most a few days, at 20° C, if there were 

 not dispersion processes in the living cell counteracting the 

 coagulation processes (8b). The proteins in vitro at the same 

 temperature require thousands of years for coagulations. 



The way investigators of colloids are attempting to change 

 our conception of the structure of living matter is well illus- 

 trated by the work on the ordinary green chloroplast. Earlier 

 work indicates a definite structure of this organ, but different 

 investigators give very different pictures. One speaks of the 

 cytoplasmic stroma as a sponge-like framework with definitely 

 organized granules of pigment filling the cavities, another of 

 the pigment itself in the framework with the protein filling the 

 cavities, and a third of the surface distribution of the pigment. 

 Liebaldt (9) has lately studied the structure of this organ 

 from the standpoint of colloids and finds that the normal 

 living chloroplast is generally homogeneous when viewed eith- 

 er with the microscope or the ultramicroscope. Allowing 



