INFLUENCE OF THE MEDIUM 131 



those of the cambium. Vandervelde 1 experimented upon 

 the germination of seeds which had been soaked twenty-four 

 hours in various concentrations of several salts. As the 

 solution became stronger the number of seeds to germinate 

 decreased, but after a certain minimum of germination was 

 reached, the number germinating again increased. This 

 author suggests that the failure to germinate in the inter- 

 mediate concentration is due to the penetration of the salts, 

 while in stronger solutions little or no imbibition of water 

 took place, and the seeds when planted were practically the 

 same as when put into the solution. This subject has been 

 recently taken up again by Buffum and Slosson. 2 These 

 authors show that not only is imbibition of seeds greatly 

 retarded by a concentrated solution (as was known before), 

 but also germination and the growth of the plant are retarded 

 in the same manner. This is true without regard to the 

 chemical nature of the dissolved substance. Both electro- 

 lytes and non-conductors were used. Retardation of growth 

 is not proportional to concentration, however, for an osmotic 

 pressure of one hundred atmospheres retards growth only 

 about twice as much as a pressure of ten atmospheres. 



Regarding the maximum concentrations in which fungus 

 growth can occur, investigations have been made by Eschen- 

 hagen and by Raciborski. Eschenhagen 3 found that this 

 maximum was different for different fungi studied, but the 

 concentration was about the same for different salts, seeming 

 to show that it was a purely osmotic effect. For Penicillium 

 the maximum concentration is about that of a five-normal 



1 A. J. J. VANDERVELDE, " Ueber den Einfluss des chemischen Reagentien und 

 des Lichtes auf die Keimung der Samen," Bot. Centralbl., Vol. LXIX (1897), pp. 337-42. 



2 E. E. SLOSSON AND B. C. BUFFUM, "Alkali Studies II," Bulletin 39, Wyoming 

 Agric. Exp. Sta. (1898) ; B. C. BUFFUM, "Alkali Studies III," Ninth Annual Report, 

 Wyoming Agric. Exp. Sta. (1899); E. E. SLOSSON, "Alkali Studies IV," ibid. (1899); 

 B. C. BUFFUM AND E. E. SLOSSON, "Alkali Studies V," Tenth Annual Report, 

 Wyoming Agric. Exp. Sta. (1900) . 



3 F. ESCHENHAGEN, Ueber den Einfluss von Losung en verschiedener Koncentra- 

 tionaufdas Wachsthum von Schimmelpilze, Stolp, 1889. 



