METABOLIC PROCESSES IX THE PLANT. 



291 



We get two flasks of about 500 c.c. capacity, a and 6, and fill a 

 >J full of water, and b full of a fermenting fluid (beer wort 

 with addition of yeast). Both flasks are fitted with three-holed 

 rubber stoppers, through each of which is passed a thermometer, a 

 leading tube reaching to the bottom of the flask, and an exit tube. 

 The flasks having been packed in wadding, the exit tube of b 

 is connected up with an aspirator, a and 6 are connected by rubber 

 tubing, and a slow stream of air is bubbled through a, and 

 then on to &. After a time we find that the fermenting fluid is 

 about 2 C. warmer than the water, and this difference of tempera- 

 ture remains when Hydrogen is led through the fluids. Yeast 

 therefore, in contrast with other plants, produces about the same 

 quantity of heat 2 both in normal and intramolecular respira- 

 tion. 



In many cases it is advisable to determine the proper tempera- 

 ture of the plants, by employing a thermo-electric apparatus. 

 This method may, e.g., be used for 

 investigating shoots, the develop- 

 ment of heat in which, generally 

 speaking, is only very trifling. I 

 was, e.g., able to show in this way 

 that living Helianthus shoots, about 

 15 cm. long, in air saturated with 

 moisture, were about 0'3 C. higher 

 in temperature than dead shoots. 

 We experiment after Dutrochet's 

 method 3 with the apparatus indi- 

 cated in Fig. 108. 



The ends of the iron loop e are 

 soldered to the copper wires o and 

 h, and the junctions, after being 

 -Carefully varnished, are pushed into 

 the shoots c and d, of which c is 

 living, while d has been killed by 

 immersion in hot water. The 

 difference in temperature between 

 the shoots is indicated by the de- 

 flection of the galvanometer inserted 

 between the ends of the wires n and 

 m. The deflection of the galvano- 

 meter corresponding with 0< 1 C. difference of temperature, 



FIG. 108. Dutrochet's apparatus 

 for thermo-electric researches on 

 plants. 



