166 SOME RECENT RESEAECHES IN PLANT PHYSIOLOGY 



Trinchieri, as regards the slightly higher pressure main- 

 tained by plants living in sunny aspects, were confirmed 

 by the experiments on Hedera. About thirty pairs of 



FIG. 21. Hedera helix: LEAVES. 



The upper pair of curves are obtained by plotting the data furnished by 

 cryoscopy of the sap pressed from leaves picked during the years 

 1912, 1913, and 1914. The cells were rendered permeable by treat- 

 ment with liquid air. The lower pair of curves are constructed 

 from data furnished by the sap of untreated leaves picked during 

 the years 1910 and 1911. In each case the broken line connects 

 the observations made on leaves from the south aspect, and the 

 full line those made on leaves from the north aspect. 



determinations made at intervals over nearly two years 

 yielded, as mean values for osmotic pressures, 9-61 atmos- 

 pheres and 9-00 atmospheres for plants from a southern 

 and northern aspect respectively.. 



