154: LIFE OF A TREE. 
The cause of this singular phenomenon is well 
ascertained. We have already seen that the 
green parts of plants absorb carbonic-acid gas 
under the influence of light: now, it is a remark- 
able fact that flowers, on the contrary, drink in 
pure oxygen gas; and it is found, that just in 
proportion as a flower consumes this gas, its heat 
rises or falls. Thus, while other flowers only 
consume eight parts of oxygen, the Arum, in 
which we have seen the heat was most manifest, 
consumed thirty parts.* As chemists well know 
that no substance can unite itself to oxygen gas, 
without producing heat, this is without a doubt 
the cause of the evolution of the heat in question. 
Although the thin bright edge of the young 
moon rises higher and higher, warning us that 
while we are lingering to tell of all the cu- 
riosities of and in connection with the tree’s 
history, the hours are rolling on; yet the warm 
still air of the midsummer evening, all fragrant 
as it is with such a mixture of sweet odours as 
* In a common fire all the heat we feel arises from the oxygen gas 
of the air uniting itself to the coal; and though the heat of these 
flowers is feeble, it nevertheless is due to the same cause, which is 
indeed commonly called Combustion. 
