234 RALPH S. LILLIE AND EARL N. JOHNSTON. 



material is transformed and accumulated, and the system will 

 undergo a cycle of chemical and physical transformation which 

 will itself be constant and specific. That is, two or more such 

 systems will undergo identical transformations. This, put 

 simply, appears to be the general property or condition which in 

 living organisms we call "heredity." 



The artificial growing systems considered in the present and 

 preceding papers exhibit in a simplified form the same general 

 type of behavior. We have seen that in a system of a given 

 composition chemical reactions occurring under structural 

 conditions of a definite kind will give rise to definite reaction- 

 products at a definite rate and in definite situations; hence if 

 solid i. e., structurally coherent and stable material is among 

 these reaction-products, this material as it accumulates will 

 add to the already existing structure in the system and will 

 itself influence in a. definite manner the succeeding reactions and 

 structure-formation. In the formation of precipitation-struc- 

 tures or crystallization-structures by combinations of mutually 

 precipitating dissolved salts this general type of phenomenon is 

 exemplified in a simple manner; and when the precipitates have 

 certain physical properties low solubility, fine subdivision, 

 colloidal quality, coherence the structures thus formed often 

 exhibit a close resemblance to simple types of organic growth. 

 Precipitation-structures of copper ferrocyanide, made by running 

 a solution of copper sulphate beneath a solution of potassium 

 ferrocyanide, have long been used to illustrate this phenomenon. 

 The essential basis for this resemblance is undoubtedly the for- 

 mation of semi-permeable membranes by the precipitate as it 

 forms; these, by preventing diffusion, furnish the conditions for 

 the osmotic entrance of water into the various membrane- 

 enclosed spaces (which are typically of a vesicular, cellular or 

 tubular form) ; a more or less definite localization of osmotic 

 processes and of the direction of flow of solution results; hence 

 the deposition of precipitate is also localized and a correspond- 

 ingly definite structure is formed; which resembles that of simple 

 vegetative growths because of the importance- of the osmotic 

 factor in both cases. The size, shape, and other characters of 

 the structures formed under these simple conditions are not so 



