demonstrating the Heat of Respiration . 437 
may register s*o centigrade above the control III. This may be taken as 
the rise of temperature due to the respiration. 
The behaviour of Flask II is most instructive. Its temperature gradually 
rises, but more slowly than is the case with I, and after two days or so it will 
be found to possess a higher temperature than that of I. This rise of tem- 
perature is due to the action of various fungi and bacteria which invariably 
gain a footing on the dead unsterilized seeds. 
As the experiment proceeds it is often found, after about a week, that 
the seeds in I are attacked by moulds and bacteria, and hence the later 
temperature difference is due partly to the seed-respiration and partly to 
putrefaction. It is only in the initial stages that the experiment gives 
a true indication of the heat evolved during respiration, unless the seeds 
have been sterilized before insertion. 
The experiment is usually kept under observation for about fourteen 
days. By taking readings at frequent intervals, say twice a day, of the 
differences of temperature between I and II and between II and III, and 
employing them as ordinates, very instructive graphs can be obtained 
showing the progress of the heat of respiration and that of the heat of 
putrefaction. 
A very simple method which yet gives excellent results and would be 
useful in school work may also be mentioned. The seeds are placed in 
three boxes instead of three flasks : ordinary chalk boxes placed upright 
answer admirably. A small hole is made at the top to serve for the 
introduction of the thermometer and suitable perforations at the opposite 
end for the escape of the C 0 2 . By this extremely simple means results 
similar to those given by Sachs’s method may readily be obtained. 
A more refined experiment may be performed by using a modification 
of the Dewar flask (Fig. b). Since 1903 I have employed flasks of this 
description with the addition of a drainage tubule, the vacuum diminishing 
very considerably the loss of heat from radiation (‘Proc. Roy. Soc., B.,’ 1908). 
These flasks are somewhat expensive and hardly suitable for students’ use. 
But they are excellent for research and demonstration purposes, and several 
sets of the simpler apparatus can easily be provided so that the students 
may set up and work out the experiments individually. 
With this form of apparatus many instructive experiments may be 
carried out. Thus by closing the end of the drainage tube in I and allowing 
the C 0 2 to accumulate the fall of temperature due to decrease of respira- 
tion under these conditions can be noted. Or by filling the flask I with C 0 2 
or hydrogen or nitrogen one may observe the failure of the seeds to germi- 
nate under such conditions and the consequent absence of any rise in 
temperature. 
Ganong (‘ Plant Physiology ’) also recommends vacuum flasks, but uses 
an alkali to absorb the C 0 2 in place of the drainage tubule. 
