RESPIRATION OF PLANTS. 



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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 which 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 Aroidese at the time of fertilisation, where (especially in warm 

 air) an excess of temperature of from 4° to 5° or even of io°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. nodi- 

 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.)] 



1 [For a collection of recorded instances of phosphorescence in plants see Hardvi^icke's Science 

 Gossip, 1871, p. 121.] See my Experimental Physiology, and Schmitz (Linnaea, 1843, p, 523) and 

 Bischoff (Flora, 1824, II. 426) on the phosphorescence of Rhizomorphs. 



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