the Transpiration-Current. 417 
The rate of transmission of water was observed while the tem- 
perature of the jacket was varied. The general results were 
as follows : — 
In cooling , the current had almost ceased at — J° and com- 
pletely at — ii° ; in warming , it recommences feebly at — 5 0 . 
It was impossible to fix upon any temperature as the actual 
freezing temperature in the lumina from the observations, but 
as all current had ceased at — n°, at which temperature the 
water in the walls was almost certainly not frozen, we must 
Woodcut 8. 
conclude that these observations reveal no current in the walls 
even of the feeblest intensity, for the method of observation is 
very delicate. However, the method is beset by the doubt 
involved in the evident ice-pressure upon the walls. 
Experiments in which the wood of Taxus was exposed to 
high temperatures — above ioo°C. — appear to show that 
coloured water can be drawn through the wood when this 
is at a temperature so high as 125 0 , and very certainly filled 
with water-vapour everywhere in its lumina. 
Woodcut 8 shows and explains the arrangement of the 
