RESPIRATION OF PLANTS. 
The combination to form carbon dioxide of the inhaled oxygen with a portion 
of the carbon of the assimilated substance is, like all combustion, accompanied by 
the production of a corresponding amount of heat; but this only rarely leads to 
a sensible increase of temperature of the masses of tissue, because respiration, and 
in consequence the production of heat, is not in general very copious, while the 
circumstances are very favourable to the loss of heat by the plant. In this respect 
also plants may be compared to cold-blooded animals. When an amount of heat 
is set free in the cells by the process of respiration, it first of all distributes itself 
over the large mass of water which permeates the cells and the adjoining tissue. In 
the case of a water-plant the least excess of temperature is at once equalised by the 
surrounding water; while in the case of a land-plant evaporation has a powerful 
cooling effect on the aerial parts, quite independently of the action of the radi- 
ation of heat which is favoured by the large superficial development of most 
plants, and especially by their hairiness. With these causes of a rapid loss of 
heat, it is not surprising that the parts of a plant w^hich are expanded in the 
air are even colder than it, although their respiration is continually producing small 
quantities of heat. But if the causes of the loss of heat are removed, it is possible 
to observe with the thermometer the increase of temperature caused by respiration. 
This can be done by accumulating rapidly germinating seeds, as is shown in the 
considerable elevation of temperature of grains of Barley in the manufacture of malt ; 
and this elevation can also be proved in the case of other germinating seeds, or 
growing bulbs and tubers. The proof is more difficult in plants with green leaves. 
In some flowers and inflorescences the production of carbon dioxide which 
accompanies the inhalation of oxygen is very energetic, the radiation of the heat 
produced being at the same time diminished by the small superficial extent of the 
organ and by protecting envelopes ; and in such cases a very considerable elevation 
of temperature of the masses of tissue has been observed. The best illustration of 
this is the spadix of Aroideae at the time of fertilisation, where (especially in warm, 
air) an excess of temperature of from 4° to 5° or even of 10° C. or more has been 
detected. Less considerable elevations of temperature have also been observed in 
the separate flowers of Cucurbita, Bignonia radicans, Victoria regia^ &c. 
In the few cases in which up to the present time the development of light or 
Phosphorescence has been observed in living plants, this phenomenon is also dependent 
on the respiration of oxygen. In Agaricus olearius (of Provence) this has been 
definitely proved by Fabre. This Fungus emits light only so long as it is alive, and 
ceases to do so at once when it is deprived of oxygen ; the respiration is in this case 
also very copious. Besides this Fungus, Agaricus igneus (of Amboyna), A. nocti- 
lucens (of Manilla), A. Gardneri (of Brazil), and the Rhizomorphs are known to 
emit light spontaneously ; the statements with respect to the light emitted from 
various flowers are of extremely doubtful value \ 
found that the proportion of nitrogenous matter in leaves gradually diminishes, while that of carbon- 
aceous matter increases, between autumn and spring. (See Revue scientifique, Aug. i, 1874.)] 
^ [For a collection of recorded instances of phosphorescence in plants see Hardwicke's Science 
Gossip, 1871, p, 121.] See my Experimental Physiology, and Schmitz (Linnsea, 1843, p, 523) and 
Bischoff (Flora, 1824, II. 426) on the phosphorescence of Rhizomorphs. 
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