Dixon — Variations in the Permeabiliti/ of Leaf- Cells. 353 



40° and 50°. The initial steepness is most marked in those with the highest 

 resistance, viz. 40-60 X 10* ohms. The final steepening, which, in some cases 

 at least, seems associated with lethal changes, is, so far as I have observed, 

 most marked in young immatui'e leaves which rapidly change colour aboiit 

 and over 40° C. (see- fig. 6). 



Over the interval of temperature used the conductivity tempex'ature- 

 coefficieut for 10° (i.e. the ratio of the condiictivity at T° + 10° to the 

 conductivity at T° C.) varied considerably, viz. from 1-70 to 0-92. The average 

 of the thirty observations plotted in fig. 4 gives 1-334 for the coefficient — a 

 figure almost identical with that obtained by Osterhout for Laminaria. This 

 figure is a measure of the variation of permeability with temperature. 



The resistance of the leaves of Eedera helix appears to grow with age, and 

 this in spite of the fact that during the interval growth in thickness takes 

 place. 



Eedera. Ml-Cx. April hf- irtL. 



A dnd B Curvvs /bi* fst fiia.tm^. 



fi! s.ndB' •■ ■• Znd. ' 



%^ l^d^ a.-nd'Bd. — . — ._ . sfUy expasu-f^ 



A e o Vouny leaf of )9A4 



10 IS 20 25 30 3S ♦» AS 

 7efn.pt^a.tv,rt. 



Fig. 5. 



5 la 15 JO us so is 40 45 so 



7e mps-T'M.EUr'a . 



Fig. 6. 



Table. 



