60 ILLINOIS ACADEMY OF SCIENCE 



departure is the Liesegang ring system. This concentric ring 

 system is produced in a few hours after placing a droplet of 80 

 per cent AgN0 3 on a 5-10 per cent gelatin plate bearing one per 

 cent K 2 Cr 2 7 . The rings consist of Ag 2 Cr0 4 and become 

 more definite and more distinct from each other as the distance 

 from the drop increases. The explanation of this phenomenon 

 is still in question, although it may be due to the colloidal sub- 

 stratum making possible great supersaturation before the labile 

 equilibrium is reached. The bands formed in gelatin in capil- 

 lary tubes show definite rhythm and polarity. Aside from the 

 Ag 2 Cr0 4 bands there are others caused by impurities in the 

 gelatin which Kuster terms small rhythms in contract to the 

 great rhythms of Ag 2 Cr0 4 . Contact with the dish in contrast 

 to free gelatin, tensions, pressures and many other conditions, 

 produce a great variety of precipitation figures. In fact pat- 

 terns can be produced that resemble closely all the various 

 structures appearing in mottled leaves, in the arrangement of 

 vascular elements of plants and the markings of tracheae. 

 Kuster emphasizes the fact that the pattern differentiation of 

 Ag 2 Cr0 4 precipitate shown in the gelatin plate is a self differ- 

 entiation occurring under constant environmental conditions. 

 This is taken to show that similar periodic or rhythmic struc- 

 tural changes in the cells may be independent of rhythm in the 

 environment, a matter of self-differentiation. The work also 

 indicates the possibility of separating such differentiation from 

 vitalistic peculiarities. The fact that a simple diffusion pro- 

 cess in gelatin gives complex polarized precipitation patterns 

 leads the author to conclude that perhaps a complex pattern in 

 the organism may likewise be referred to a simple diffusion 

 process in a colloidal matrix rather than explained by appeal 

 to complex regulative action of living protoplasm. 



Rhythm in plant activity is held by many to be generally re- 

 lated to environmental rhythm. Others feel that rhythm is a 

 necessity of the very nature of protoplasmic activity; activity 

 must be followed by rest. An examination of the facts that 

 Kuster offers shows the possibility of rhythms in the organism 

 independent of the inscrutable features of protoplasm. In 

 short, internally determined rhythms may be matters of rela- 

 tively simple physical and chemical laws. Bringing this third 

 possibility of structural rhythm and polarity into prominence is 

 the great contribution here. The work really has not explained 

 in terms of process of formation a single plant or animal struc- 

 ture. 



If the explanation of Ostwald mentioned above is correct, 

 it means that a colloidal medium of the type of a gel favors 



