400 TRANSFORMATION OF ENERGY 



excess of heat as any other plant organ. The great evolution of heat takes place 

 on the opening of the spathe towards evening ; this increases rapidly in intensity, 

 reaching a maximum just before midnight. Next morning the temperature 

 has again become equal to that of the air and remains so. In Victoria regia 

 the rise in temperature commences about nine hours before the opening of the 

 flower, and rapidly increases to a maximum after the flower opens (i. e. towards 

 evening). Then in the night ensues a reduction in temperature, followed by the 

 attainment of a second lesser maximum on the evening of the second day (Knock, 

 1899). Periodicities such as these have been observed in all cases where the pro- 

 duction of heat continues for some time. The maxima do not always occur ex- 

 actly at the same hour from day to day, but they occur during the day hours, 

 before or after noon, apparently never at night. The immediate cause of this 

 periodicity is naturally closely connected with periodic variations in the en- 

 vironment, but in what respect temperature operates has as yet not been exactly 

 ascertained. 



The relation existing between respiration and the production of heat is a 

 close one. The experiment with germinating seeds, referred to above, is successful 

 only if a sufficient amount of oxygen is permitted to enter the vessel. It has 

 also been long known that the consumption of oxygen increases pari passu with 

 the rise in temperature, and that it is excessive in flowers and inflorescences, 

 which develop large amounts of heat. Garreau (1857) carried out accurate 

 experiments on Arum italicum, and demonstrated an almost perfect correspon- 

 dence between the absorption of oxygen and the rise in temperature. On the 

 other hand, Erikson (1881) showed that on the exclusion of oxygen, and after 

 in tra-molecular respiration had begun, the temperature scarcely exceeded that of 

 the air outside. In Arum, for example, he was able to demonstrate in in tra-mole- 

 cular respiration, an excess of only 0-3° over the normal respiratory tempera- 

 ture of 16-5°, and in Raphanus seedlings 0-2° C. over the normal 57° C. 

 Again, in cases of fermentation conducted under anaerobic conditions, a very 

 obvious increase in temperature occurs in the fermenting substance. Erikson 

 found that fermenting yeast, under definite experimental conditions, showed a 

 rise of temperature of almost 4°, while the same yeast gave an increase of only 

 o'2° when milk-sugar was provided instead of grape sugar ; moreover, no fer- 

 mentation could be induced. This result agrees with that previously established, 

 viz. that growth (and we may assert the same of movement also) cannot be 

 carried on in ordinary plants by intra-molecular respiration only, although, by 

 fermentation, it is quite possible in anaerobes. When we finally remember that 

 increase in respiration (p. 202) has also been observed as a result of the action 

 of traumatic factors (Richards, 1896) we may consider the relation between 

 respiration and heat production as sufficiently well established. 



These relationships can be most readily explained by assuming that respira- 

 tion and the related process, fermentation, are the sources of the heat evolved. It 

 has been already clearly pointed out that chemical energy must be released when 

 organic substances are oxidized or other chemical decompositions are effected, 

 and this release of energy affords an explanation of the processes under con- 

 sideration. It needs no proof to establish the view that the energy so released 

 must in whole or in part appear as heat, since in everyday life we employ this 

 method for obtaining it. Still, it may be asked whether respiration is sufficient 

 to account for the amount of heat production which has been observed. This 

 question has been answered only by Bonnier (1893), who compared the actual 

 amounts of heat produced with the theoretical amounts arrived at by calculating 

 the oxygen absorbed or the carbon-dioxide given off. Should Bonnier' s results 

 prove correct — and it is advisable that they should be confirmed — it would 

 appear that more heat is actually produced in the germination of many seeds 

 than can be accounted forby respiration. There are other processes in the plant 

 which might aid in the production of heat, such as the solution of solids, the 



