produced in the Atmosphere by Colocasia odora. 163 



ance of oxygen, and its being replaced by carbonic acid gas, was 

 the cause of this ; the quantity of oxygen gas in the jar being 

 once absorbed, the development of heat, losing the stimulus 

 which is indispensably requisite for its existence, must neces- 

 sarily discontinue. 



Judging that by this experiment we have nearly arrived at 

 the right explanation, we think that our former experiments, 

 especially the one of 1838*, concerning the influence of ni- 

 trogen on the spadix of the species here alluded to, must be 

 brought into connexion with it. There was then no develop- 

 ment of heat whatever, the oxygen gas being wanting ; here 

 it had entirely ceased after a few hours, because all the oxygen 

 gas was absorbed from the atmosphere. On considering this 

 phaenomenon, the question readily presents itself, — does the 

 oxygen liberating caloric combine with the carbon contained in 

 the plant to form carbonic acid, and is thus the development 

 of heat, combustion ? We are inclined to think so ; for when 

 the development of heat has reached its maximum, which is 

 the case in the middle of the day, then also the alteration which 

 the enclosed air undergoes is greatest, as was proved by an 

 experiment we purposely made on the 27th of last June. 

 With this view, we placed at that time in the apparatus, in 

 which a spadix was enclosed, some potash, in order to ab- 

 sorb the carbonic acid in the same ratio in which it was pro- 

 duced. During the time the absorption was taking place, we 

 saw the mercury rise several inches within the space of one 

 hour. 



As yet we had made these experiments with the same sort 

 of thermometer we had previously used ; but we wished to re- 

 peat them with a thermo-electrical apparatus : for this pur- 

 pose we procured one of M. Becker, philosophical instrument 

 maker in Groningen, who last year, after the flowering of our 

 Colocasias, constructed a most excellent and delicate instru- 

 ,ment of this description, with the physiological needles of 

 Becquerel appended to it. 



On making these and other experiments, we found, that al- 

 though the increase of temperature was not quite impercep- 

 tible on the second day, yet it was too trifling to attach any 

 particular value to it. On this ground we think we may state, 

 that on the first day all the oxygen gas had not been com- 

 pletely absorbed. 



The experiments with the thermo-electrical apparatus, and 

 also all the former ones, were taken in a room of nearly an 

 equal temperature. Either in the dark or in the light the 



* Vid. Tijdsclir. voor Nat. Gesch. en Physiologie, Deel V., p. 222. 



.M 2 



