308 LECTURE XIV. 



We have now sufficiently established the connexion 

 between the evolution of heat and destructive metabolism, 

 but we may briefly consider the fact which is apparent in 

 the tables given above that the evolution of heat is not 

 constant but variable. In opening flowers there is a period, 

 varying in length in different cases, of active destructive 

 metabolism ; at the commencement of this period the evolu- 

 tion of heat is small, but it gradually rises to a maximum, 

 and sinks again to a minimum. This we may term the 

 " grand period" of the evolution of heat. 



In illustration of this, Kraus' observations, made by means of a 

 thermometer on the temperature of the spadix of Arum italicum, may be 

 quoted. It may be mentioned here that the evolution of heat is greatest 

 in the sterile portion of the spadix (Dutrochet, Kraus), less in the portion 

 bearing the staminal flowers, and least in that bearing the pistillate 

 flowers. Only the excess of the temperature of the spadix over that of 

 the atmosphere is given in the table : the temperature of the air varied 

 between 15-3 C. and 16-3 C. 



Kraus. 



4.15 p.m. o'9C. 7.30 p.m. ii -3 C. 



4.25 -- 1-3 *8 11-9 



5 2-2 8.15 12-15 

 5-30 5'4 8.30 12-00 

 5.45 7'o 8.45 i r8 



6 8-2 9-30 1 1 '3 

 6.30 8'6 10.20 10-6 

 6.45 -- 9-0 ii 10-4 

 7.2 97 i a-m. 8-0 

 7.15 10-5 6.30 0-2 



When the period of active destructive metabolism is 

 prolonged the evolution of heat exhibits a diurnal variation, 

 which might be indicated graphically as a secondary curve 

 on the curve of the grand period. 



The following are some observations of Dutrochet's on the spadix 

 of Arum maculatum^ made by means of a thermopile : they extend over 

 the whole grand period, and illustrate the relation of the daily periods to 

 the grand period : the figures give the difference between the temperature 

 in the spadix and that of the air ; when a minus sign is used, it means 

 that the temperature of the spadix was lower than that of the air. 



