Dixon and Atkins — Osmotic Pressures in Plants. 



459 



The coucentration of the electrolytes accounts for about 4 atm. of the 

 osmotic pressure, the remaining 8-15 atm. are due to the soluble carbohydrates. 

 The principal fluctuations also are due to variations in the carbohydrates 

 content, with the exception of the erratic records just alluded to. 



NOV DEC. -JAN. FEB. MAR. APRIL MAY JUNE JULY AUG. SEPT. OCT NOV. 



Hedera .helix. — Mature leaves. S. aspect. 

 Fig. 5. 



The two dotted graphs in the figures show that the sap pressed from the 

 untreated leaves has, as is generally the case, a lower osmotic pressure, but 

 at the same time exhibits a marked diminution in concentration during the 

 summer months. 



