565 
Electrolytes upon Cells of Saxifraga umbrosa . 
one experiment was carried out at 9 0 C. owing to the difficulty of main- 
taining a steady temperature by the means available, viz. the addition of small 
quantities of ice-cold water to the thermostat of tap-water. The tempera- 
Fig. 1 . Influence of change of temperature upon permeability to K 2 Cr 2 0 7 . Concentration 
- 3 %. T = time in hours to produce precipitate. 
ture effect showed the advisability of keeping strictly to one value through- 
out the tests, although the errors due to slight fluctuations of the room 
temperature in earlier work were probably small compared with those due 
to * past history ’ factors. 
Preliminary Treatment of Material and Immersions. 
The plants used for this portion of the work were all grown in the 
same soil. For winter use specimens were kept in a cool greenhouse and 
rosettes cut and kept in water in the laboratory for one day before the 
sections were made. Long strips were torn from the petiole and kept for 
twenty-four hours in a large quantity of distilled water, which was changed 
at intervals. It was found to be extremely important to select leaves of 
the same condition, and those from the base and apex had to be rejected. 
Doubtless the differences in the cell-walls modified diffusion. On account 
of lack of similar material in two or three of the tests quoted it will be 
found that fewer values than the usual number had to suffice. 
On preliminary examination of the material with 1 per cent, caffeine 
it was found that a greater number of cells had tannin contents than had 
