GENERAL 



371 



A copper or German-silver wire (<?, Fig. 66) is smelted to two iron wires (m, n). 

 The tips, covered with shellac, are embedded, one in the living shoots, the other in 

 a dead one (d) held up by a thread (s). The whole is covered with a bell-jar, and 

 the current measured by means of a reflecting galvanometer. In this way a difference 

 of temperature of -5 JVC. can be detected and the temperature at different points on 

 the same plant can be compared. 



For quantitative experiments various forms of calorimeters may be used, of 

 which several have been especially adapted for animal physiology 1 . Rodewald 



FlG. 65. Apparatus for showing the 

 influence of oxygen upon the production 

 of heat : (a) contains the germinating 

 seeds ; (b) thermometer; gases can be drawn 

 through at (c). 



FIG. 66. Apparatus for thermo-electric 

 measurement of temperature : (c) living, 

 (cf) dead shoot ; (e) German-silver wire ; 

 (MI and n) iron wire ; at o and e the thermo- 

 electric junctions are inserted in the shoots. 



determined the absolute temperature thermo-electrically, and then estimated from this 

 the amount of heat required to balance radiation and transpiration. This method 

 is, however, liable to lead to serious error owing to the difficulty of control. 



The difference between the heat of combustion of the seed and of the dried 

 seedling grown in darkness gives approximately the amount of heat liberated during 



T. xiil, p. 5 ; Rodewald, 1. c., 1887, p. 276 ; 1888, p. 221 ; Seignette, Rev. gen. de Bot., 1889, T. I, 

 p. 574; Richards, Annals of Botany, 1897, Vol. xi, p. 31. On methods see also Cyon, Methoden 

 der physiologischen Experimente, 1876, p. 484; Hermann, Handbuch d. Physiologic, 1882, Bd. iv, 

 T. II, p. 305. The bolometric method has not yet been used for determining temperature in plant 

 physiology. 



1 See Rubner, Die calorimetrische Methodik, 1891; Traite de physique biologique, public p 

 d'Arsonval, &c., 1901, p. 804. 



B b 2 



