METABOLIC PROCESSES IN THE PLANT. 289 



temperature of the fluids. It is found that that contained in the 

 cylinder A is 1 or 2 C. warmer than the water in the cylinder 

 B. 



In searching and accurate investigations 011 the proper tempera- 

 ture of plants we may conveniently use a respiratory vessel such 

 as is indicated in Fig. 97, of about 200 c.c. capacity, and provided 

 with a spiral tube. We require two of them. One we fill with 

 four to five days old wheat or barley seedlings, grown in sawdust, 

 the other with seedlings which have been killed by immersion in 

 boiling water to which some Salicylic acid has been added. The 

 two vessels are connected with one another by means of rubber 

 tubing ; they are provided with carefully compared thermometers, 

 completely packed in cotton wool, and placed in a wooden box. 

 This is put in a room with a north aspect, in which the tempera- 

 ture varies little. The vessel containing living plants we put in 

 connection with an aspirator, and lead a slow stream of air 

 saturated with moisture over the research material. The air 

 enters through the spiral tube of the vessel containing the dead 

 seedlings. The observations of temperature made from time to 

 time (say every half-hour) indicate that the fresh material 

 rapidly assumes a temperature of 2-3 C. higher than the dead 

 material. These last do not develop heat, while the living 

 seedlings undergo a considerable rise of temperature. 



We will now pass through the apparatus for about an hour a 

 rapid stream of Hydrogen (the gas is purified by being passed 

 through a wash bottle containing Potassium permanganate and 

 potash solution). This being done, we close the stop-cock H Jf 

 (Fig. 97), and also a stop-cock on the spiral tube of the vessel 

 containing dead material. The vessels, still packed in cotton wool, 

 are left alone for a few hours only. The elevation of temperature 

 in the living seedlings is now, since the respiration is intramolecu- 

 lar, only very slight, about '2-0 '3 C. ; it rapidly rises, how- 

 ever, to 2-3 C. when air is again led through the apparatus. 



Observations on the heat developed by seedlings in normal 

 respiration sh&Ved me also that it is greater the nearer the tem- 

 perature at which we are experimenting approaches the optimum 

 (40 C.). This is quite natural, because, with rising temperature, 

 metabolism and respiration in the plant-cells (and therefore also 

 development of heat) are more active than at lower temperatures. 



When we supply the apparatus not with seedlings, but with 

 adequate quantities of the spadices of Arum maculatum, the 



P.P. U 



