484 



BOTANICAL GAZETTE 



[DECEMBER 



the factor, or combination of factors, responsible for the difference 

 acts differently or with different intensities at night than during 

 the day. 



CHART VIII. 



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1911. 



Among the plants used* the water lily offers perhaps the fairest 

 comparison, since the floating leaves are but slightly elevated above 

 the water surface and physical conditions are thus nearly equal for 



