282 On (he Structure and Functions of the Organs of Respiration. 



the temperature of the spadix rose as much as fifty-two degrees above that 

 of the surrounding atmosphere. 



From the absence of a nervous system in vegetables, it would appear 

 that the development of heat during germination and flowering, is to be 

 considered as a strictly chemical effect, arising from the combination of 

 carbon and oxygen ; and if so, we ought to find signs of disengagement of 

 caloric by all flowers. It is, however, to be remembered, that in by far 

 the greater number, the heat is carried off by the atmosphere, the instant 

 that it is developed ; and that it is only where flowers are collected in 

 great numbers within cases, which act as non-conductors, and confine the 

 heat, as happens in Arums, that the elevation of temperature becomes ap- 

 preciable. 



Some curious observations have been made on the chemical actions of 

 fruit, which tend to confirm the views just stated. During the formation 

 and ripening of fruit, it sustains a considerable loss of carbon, which com- 

 bines with the oxygen of the air ; and when placed in an atmosphere de- 

 prived of oxygen, this function is suspended ; and, if the fruit remains at- 

 tached to the tree, it dries up and dies. When fruits, separated from the 

 tree, but capable of completing their own ripening, are placed in media 

 free from oxygen, they do not ripen j but the power is only suspended, 

 and may be re-established, by placing the fruit in an atmosphere capable 

 of taking carbon from it. It appears also that the presence of oxygen is 

 essential to the rotting or decay of fruits. The extrication of carbon ap- 

 pears due, as in germination and flowering, to the conversion of gum, and 

 other proximate principles, into sugar. 



Some interesting experiments have recently been made by Marcet, on 

 the effects of plants not coloured green upon the atmosphere. He found 

 that growing mushrooms absorb from the air a large quantity of oxygen, a 

 portion of which appears to combine with the carbon of the plant, and is 

 given off in the form of carbonic acid ; whilst the rest seems to be fixed in 

 the vegetable, and to be re-placed, at least in part, by nitrogen disengaged 

 from the mushroom. Here then we have an example of the influence of 

 respiration, unaccompanied by digestion; for it appears that the large 

 quantity of carbonic acid disengaged from the soil in which these vegeta- 

 bles thrive, renders it necessary that the superabundant carbon of the plant 

 should be constantly removed by the atmosphere, instead of any addition 

 being received through that medium. 



The changes which are effected in the leaves of plants, upon the sap 

 brought into them by the upper stratum of veins, seem to consist chiefly 

 in the elaboration of the proper juice, which flows back along the lower 

 stratum, and descends towards the roots, through the bark, in which va- 

 rious secretions are deposited ; part, however, being carried inwards by 

 the medullary rays to the duramen, or heartwood. 



We have seen that the organs of respiration in animals are formed on 



