332 The Ohio Journal of Science [Vol. XIX, No. 6 r 



similar conditions. Evaporation from the free water surface 

 must similarly affect the concentration of salts. The ash 

 contains such small amounts -of the soluble salts necessary for 

 plants that it may be supposed that only where concentrated 

 by evaporation do they occur in amounts sufficient for vigorous 

 growth.* 





Photograph by Robert F. Griggs 



CALAMAGROSTIS LANGSDORFII APPEARING IN AN AREA WHERE 

 WATER, COMING TO THE SURFACE, MAY HAVE ITS 



SALTS CONCENTRATED BY EVAPORATION. 



Surrounding pumice flats, where the surface is protected from evaporation, 



are bare. 



If this reasoning is correct, it would explain the decided 

 advantage of the plants in the wettest places over those on the 

 general surface of the ash where the loose top layer, acting as a 



*Dr. Shipley, in the sixth paper of this series, has reported that the total 

 soluble salt content of the ash is in general not especially low. But in analysis 

 directed particularly toward the solution of this question, Professor C. W. Foulk, 

 found that in the ash at Kodiak the amount of available (*'. e., water soluble) 

 potash was only 0.05%, which is exactly the amount given by Hilgard as the 

 minimum concentration requisite for plant growth. Phosphoric acid was present 

 in an even smaller amount, which Professor Foulk described as slightly more than 

 a trace, although it was so small that he made no attempt to give it a numerical 

 value. The high salt content found by Shipley is probably made up, theiefore r 

 of salts not important to the growth of the plant. 



