EMULSOIDS 301 



mate ; after a short time concentric rings of silver chromate 

 are deposited around the original drop ; this experiment has 

 given rise to much experimental work with other reagents 

 under varying conditions and there is much speculation re- 

 garding the true explanation of the phenomenon. There is, 

 however, no doubt that the experiment illustrates the possi- 

 bility of diffusion of a crystalloid such as silver nitrate in a gel. 



The bringing about of such periodicity, as is exhibited by 

 the alternating layers of deposit and clear solution in an 

 inanimate system without variations in external conditions 

 such as temperature changes, has an important bearing on 

 biological and other natural problems; it would appear to 

 offer a possible explanation of the stratification observable in 

 agate and its possible significance in connection with the 

 many concentric ring structures or other alternating deposits 

 found in nature will be obvious ; in illustration the formation 

 of starch grains may be mentioned. According to Kiister * 

 many plant structures such, for example, as the banded pith 

 of Magnolia grandiflora, the calcium oxalate sacs of Ficus 

 carica, the regular alternation of crystal bearing zones with 

 those containing no crystals found in the bark of the Pome- 

 granate and the zebra-like pigmentation of the succulent 

 leaves of Haworthia fasciata and Aloe varigata may be due 

 to similar causes ; these structures at any rate may have their 

 origin in some analogous internal rhythmic stimulus. 



The peculiar concentric growth of certain moulds resulting 

 in structures closely resembling the Liesegang rings have been 

 studied by Munk.f 



THE NATURE OF GELS. 



As already pointed out above, emulsoids are regarded as 

 two-phase systems in which the disperse phase is a more con- 

 centrated solution, and the continuous phase a relatively dilute 

 one. When such a solution gives a gel, the roles of the two 

 phases are assumed to be changed, resulting in a sort of net- 



'"-' Kiister : " Beitrage z. Entvvicklungsmechanischen Anatomic d. Pflanzen, 

 Jena," 1913. 



t Munk : " Centralblatt fur Backteriologie," 1912, 32, 353 and 34, 561 ; also 

 " Biol. Centrall.," 1914, 34, 621. See also Liesegang " Naturwissensch Woch- 

 enschr.," 1913, [xii], 25. 



