146 life's beginning on the earth 



examples are the beautiful structures appearing on the wings 

 of butterflies, and also the regular stripes appearing on 

 many leaves. Formerly many complicated assumptions 

 were made to explain the origin of such stripes ; for instance, 



ti y^CoSG^ 



Fig. 57. Inhibition of the Development op an Artificial Structure if 

 Growing in a Highly Concentrated Solution 



These two containers were filled with a dilute copper salt solution but 

 the one on the right side had also 20 per cent of ordinary sugar added to it. 

 Pieces of yellow prussiate were placed in both at the same time. The 

 photograph shows that no development occurred in the solution to which 

 sugar had been added. Obviously the sugar exerted an osmotic counter- 

 pressure preventing the development of an osmotic structure. 



This is another demonstration that osmotic forces are the important 

 factors in the development of these structures. If gravity were a factor, 

 the sugar would increase the development since, on account of the heavier 

 weight of the sugar solution, it would have allowed the structure to Moat 

 up. (One-half natural size.) 



a periodic supply of food material. No such assumption is 

 needed. Striking periodic stripe formation can be made 

 artificially when all the factors involved are kept constant, 

 or at least do not undergo periodic variations timed with 



