314 Journal of Agricultural Research voi. xii. no. 6 



At this same period Gola {18-21) published the first of his ecological 

 and chemical studies on the relation of the soil solution to the natural 

 plant environment. He attempted to obtain, by a method founded on 

 that of Schloesing (46,47), an extract which would be similar to the 

 actual soil solution. The soil was broken up so that it would pass 

 through a 2-mm. sieve and was placed in a glass cylinder, 25 cm. high 

 and 4.5 cm. in diameter. A gentle rain of distilled water at the rate of 

 25 to 30 mm. per square centimeter per 24 hours, was then allowed to 

 fall upon it. After a period of time, which varied with the soil, drops of 

 solution issued from the lower tubulure, and the process was allowed to 

 continue till 25 to 50 c. c. of "pedolytic" solution had been collected. 

 Gola then subjected the saturated soil to pressure and collected what 

 be called the "pedopiezic" solution. 



The total solids, and in some cases the total colloids, were determined 

 in these solutions. From the figures so obtained Gola divided up the 

 possible habitats of various plants into some 32 groups which he believed 

 to be controlled by the solution naturally occurring in the soil. In gen- 

 eral, he concluded that the relation between the soil and the organs of 

 absorption of the plant was controlled by the osmotic pressure of the soil 

 solution. High concentrations, and, especially, rapid changes in the 

 solution were likely to be harmful to plants, though many may grow 

 successfully in weaker solutions than were normal for them. The prin- 

 cipal factor determining the habitat of plants was the concentration of 

 the solution and, to a lesser extent, its chemical composition. 



Snyder (55, 54), at Minnesota, carried on a short series of investiga- 

 tions in which he studied the absorption of nutrients from soil extracts 

 which were added to sand cultures, believing this condition comparable 

 to the absorption from the soil water. He arrived at conclusions op- 

 posed to those of Whitney and Cameron (61) and also criticised their 

 results from theoretical considerations. 



Gedroitz (16), working in Russia, announced that the concentration of 

 the soil solution fluctuated so rapidly that it was impossible for any 

 water extract to give any indication of the character of a soil. 



Mitscherlich (42) issued an extremely valuable contribution to the 

 study of the water extract. His method of procedure was essentially 

 different from those previously discussed. He employed for the extrac- 

 tion carbon-dioxid-saturated water at 30° C, the maximum temperature 

 which would probably be encountered in the soil. The proportions of 

 soil and water varied from i to 5 up to i to 30. At least two dilutions 

 were used in each study, generally i to 10 and i to 25. The soil and 

 water were placed in a thermostat, with a stirring apparatus running 

 into the center of the flask. Carbon dioxid was passed in constantly 

 and the extraction allowed to continue for ii^ hours. 



From the data obtained by these varied extractions Mitscherlich 

 graphically estimated the amounts of additional material which were 



