OSMOTIC PRESSURES AND ELECTRICAL CONDUCTIVITIES 151 



plants have but little claim to consideration except as 

 minor limits. However, as they stand, Cavara's values 

 for the osmotic pressures of leaves vary on an average 

 from about 6 to 14 atmospheres. Extreme values range 

 as high as 30 atmospheres. This estimate does not include 

 the salt lagoon plants, which will be considered later. The 

 following table is quoted from Cavara : 



TABLE XXXIV. 



OSMOTIC PRESSURES OF LEAVES AND OTHER ASSIMILATING TISSUES. 



Cavara's comparative studies of the variation of osmotic 

 pressure hi the zones from the apex downwards are 

 also of interest. He examined in this manner Opuntia 

 amyclcea, 0. ficus-indica and Agave americana, and ascer- 

 tained that in each case the pressure fell slightly from the 

 region of the apex downwards for some distance, but rose 

 to about its former value in the basal portions. Some- 

 what similar experiments were carried out subsequently 

 by Nicolosi-Roncati (1907), who in addition measured 

 electrical conductivities; accordingly, his values only are 

 quoted. 



