724: 



TRANSACTIONS OP SECTION K. 



water through the protoplast was obtained by measuring the tangent of the 

 slope of the appropriate curve at several specified stages of plasmolysis. For 

 comparing the rates of permeation at different temperatures, values obtained 

 from corresponding stages in plasmolysis were alone used. Thus for dandelion 

 scapes at mid-plasmolysis, the rates were : — ■ 



1 2 3 5 8 12 and 22 at 



8° 14° 19° 26° 29° 34° and 42° C. 



The temperature effect thus seen is much greater than that observed by van 

 Rysselberghe, who by measuring the contraction of pith cylinders in plasmo- 

 lysing solutions at different temperatures found comparatively little difference 



Curves sJiowing the effect of temperature on permeahility of protoplasm. 



AA. Pith experiments of van Rysselberghe. 



BB. Piloholus (sporangiophores). 



CC. Dandelion (scane of inflorescence). 



in the rates above 20° 0. It is comparable with the results of Lepeschkin, who 

 observed the effect of temperature on the rate of secretion of water-drops by 

 the sporangiophores of Piloholus, and thence deduced the effect on the perme- 

 ability of protoplasm. These results are expressed graphically in the curves 

 A (van Rysselberghe) and B (Lepeschkin) ; the curve C is derived from the 

 figures quoted above for dandelion scapes. 



From the curve of rates of permeation for dandelion, the following 

 coefficients of acceleration of rate for a rise of temperature of 10° C. can be 

 calculated : 



10° to 20° C. 

 20° to 30° C. 

 30° to 40° C. 



2-5 

 2-5 

 2-3 



From Lepeschkin's data, the corresponding coefficients for these temperature 

 intervals are found to be 2'2, 1'7, and 2"! respectively. Van Rysselberghe's 



