36 Richards. — The Evolution of 
nature. The apparatus consisted simply of two bell-glasses 
of about ij litres capacity, protected all around with a thick 
layer of cotton-wadding. The bell-glasses were also supplied 
with thermometers, which had previously been compared, and 
a small aperture, loosely stopped with a bit of cotton to 
prevent any rapid circulation, was provided for the admission 
of air. Inside the bell-glasses were also dishes of KOH for 
the absorption of the C0 2 respired, and above these the plants 
were supported. After filling both of the bell-glasses, a day 
was allowed for them to become equalized in temperature. 
If readings taken in the evening and again the next 
morning both showed no difference between the two bell- 
glasses, the plants in one of them were cut and then returned 
as quickly as possible. After this the difference betvveen the 
temperatures in the two bell-glasses registered the effect of 
the injury, and readings taken from hour to hour showed the 
curve. It is unnecessary to say that these experiments were 
carried on in the room the temperature of which only on one 
or two occasions varied within a few tenths of a degree. The 
difference in the temperatures between some of the experi- 
ments is due to a difference in location of the bell-glasses. 
When on a higher level they were naturally somewhat warmer. 
For this reason the thermometers were carefully adjusted to 
the same level and never moved during the course of any one 
experiment. The amount of heat arising from the absorption 
of the C0 2 by the KOH was not regarded, although of course 
it was greater in the injured than in the uninjured plants. 
But this is counterbalanced by the fact that the warmer bell- 
glass must also lose more by radiation than the cooler. 
The apparatus was not intended to be more than approxi- 
mately accurate, and the application of such corrections 
would not be worth while for the results required. 
Although potatoes were used more than any other plant, a 
variety of others representing different sorts of tissue were 
experimented with. But potatoes were more convenient, 
and also had the great advantage of resisting the attacks of 
fungi better than anything else. The writer had also ex- 
