194 BOTANICAL GAZETTE [SEPTEMBER 
It can be used only as a food material, only by chlorophyll-containing 
cells, and by these only in the light. 
The other features of the process of respiration are hard to demon- 
strate, hard even to study. The chemistry of respiration is scarcely 
less difficult than the chemistry of photosynthesis.t Whatever the 
reactions may be in the chain which connects the free oxygen of the air 
with the oxygen combined with carbon or iron or sulphur, etc., it is 
clear, on theoretical grounds, that the oxidation or oxidations which 
take place must liberate heat. The demonstration of this fact, 
with reasonably small quantities of living organisms, has hitherto 
been nearly impossible. For this reason, it has been almost useless 
for the teacher to insist that the liberation of heat, the setting-free of 
energy, and not the material products, is the essential end, the funda- 
mental characteristic of respiration.? 
The apparatus of BoNNIER,? which has furnished the most satis- 
factory results so far in the study of the heat-yield, is too elaborate 
and too costly for most botanical laboratories. On the other hand, 
the simple appliances described and figured in the laboratory manuals 
are useless, for they do not illustrate the subject, but mislead the 
student. Using the ordinary apparatus and the usual quantities of 
live and dead peas, for example, one obtains, with good luck, 4 differ- 
ence of o°5 C. between the live and dead peas in the course oF 
twenty-four hours, or perhaps a whole degree, or, best of all, 1°5- 
This is mortifying enough, but if the temperature of the laboratory 
fall much, so that all the peas are chilled, there will be practically no 
difference at all. The evidence of the experiments, therefore, 15 all 
against the teacher who would have it that respiration is the gees 
of supplying the living thing with the energy it needs to do its ba paaiad 
Evidently the trouble is with the insulation of the vessels in which the 
respiring and the dead plants or parts are contained; for if radiation 
and absorption were reduced to a minimum, the live and — 
peas would certainly grow warmer, while the dead peas W® 
remain at the same temperature or grow slightly cooler. 
t See BARNES, C. R., The theory of respiration. Bor. GAZETTE 39:81-98 19° 
? See, for example, Petrce, G. J., Textbook of plant physiology, chaP- er vit 
3 Bonnier, G., Recherches sur la chaleur végétale. Ann. Sci. Nat. 
18: 1893. 
