GENERAL 369 



sumed in respiration other substances may also be oxidized, and in addition 

 to carbonic dioxide and water other substances may be formed in variable 

 amount with different or in some cases unknown caloric equivalents. The 

 production of carbon dioxide and absorption of oxygen does not, therefore, 

 form a sure guide as to the amount of chemical energy liberated, and hence 

 we are unable to decide how much of this energy is set free in the form of 

 heat and how much appears as mechanical work. 



Rodewald 1 found that in such resting organs as ripe apples and the 

 swollen stems of the cabbage turnip (Kohlrabi) the amount of heat produced 

 represented practically the whole of the energy of respiration, as determined 

 from the production of carbon dioxide and absorption of oxygen, and 

 .assuming that these represented so much completely oxidized carbohydrate 

 material. According to Bonnier 2 , however, seedlings of the Pea liberate 

 more heat than is represented by their respiratory activity. During later 

 stages of development the difference is lessened, and during flowering the 

 actual liberation of heat becomes less than the theoretical values. 



Bonnier suggests that during germination, in addition to respiration, 

 other chemical changes and dissociations of exothermic character occur in 

 abundance, while at a later date, especially during the storage of reserve- 

 materials, endothermic condensations and polymerizations take place which 



involve an absorption and storage of heat. The respiratory quotient (-^r^) 



is actually less than unity during germination, especially in the case of oily 

 seeds, but the subject is worthy of further investigation. In any case the 

 difference between the actual and estimated production of heat is not due 

 to the work done during growth, since the excess of the actual production of 

 heat over the theoretical amount is greatest during the period when growth 

 is most active. Furthermore the mechanical equivalent of heat is very high, 

 so that a small absorption of heat would represent an enormous amount of 

 work. Ewart has, for instance, shown that the work done in maintaining 

 streaming in a large cell of Nitella for a year represents the heat produced 

 by the complete combustion of ^Winnr of a gram of cane-sugar, the work 

 done being 252 ergs per day. In smaller cells more energy is consumed in 

 streaming, but even then the work done is insignificant compared with the 

 heat produced by respiration 3 . 



1 Rodewald, Jahrb. f. wiss. Bot., 1888, Bd. XIX, p. 291 ; 1887, Bd. XVIII, p. 342. 



2 Bonnier, Ann. d. sci. nat., 1893, 7' se*r., T. xvni, p. i ; Bull, de la Soc. hot. de France, 1880, 

 T. xxvii, p. 141. 



8 Ewart, Protoplasmic Streaming in Plants, 1903, p. 27. [i gram-calorie is the amount of heat 

 required to raise a gram of water i C. in temperature, a kilogram-calorie the amount needed to raise 

 a kilogram i C. If the expansion of water were uniform the value of the calorie would be the same 

 at all temperatures, and this is practically the case between 4C. and iooC. As regards the 

 mechanical equivalent of heat i gram-calorie represents 42,350 gram-centimetres, or 4.17 x io 7 ergs 



PFEFFER. Ill 



