290 PHYSIOLOGY OF NUTRITION. 



spathes of which have just opened (one vessel with dead, the other 

 with living spadices), we find the elevation of temperature in 

 normal material to be in intramolecular respiration about 0'2 C., 

 but in normal respiration 10-15 C. 



Exhaustive researches on the proper temperature of flowers 

 have been carried out by Dutrochet, Hoppe, G. Kraus, and many 

 others. We use for the purpose pot plants of Colocasia cordi- 

 f olium or of Arum maculatum, put into pots with the balls of earth 

 in the spring, a good time before flowering. The plants are placed 

 in diffused light in a room with a north aspect, and liable to as 

 little variation of temperature as possible. The rise of tempera- 

 ture of the flowers cannot be easily determined till the sexual 

 organs have come to maturity, and the spathes open. It can even 

 be detected by simply placing a sensitive thermometer, e.g., against 

 the spadix. 



It is better to experiment as follows. The spadix of an Arum 

 is forced a little out of the spathe, and laid against the cylindrical 

 bulb of a sensitive mercurial thermometer, supported by a suitable 

 stand. The spadix is fixed against the thermometer by means of 

 'a thin rubber ring. We may* also place the upper end of the 

 spadix in contact with a thermometer, whose mercury reservoir is 

 in the form of a double- walled bell. It is also naturally of import- 

 ance to determine accurately the temperature of the air in the 

 room. It is found that the structures investigated are warmer 

 by some degrees (Centigrade) than the surrounding air. In obser- 

 vations extending over some time (several days) we find that the 

 difference between the temperature of the air and of the part of 

 the inflorescence is not exactly the same at all times of the day. 

 The difference is usually greatest at a particular time in the 

 afternoon. We find, therefore, what is very remarkable, a daily 

 periodicity in the temperature of the flowers.* 



If it is required to prove merely in a general way that in the 

 inflorescences of Aroids a very considerable development of heat 

 takes place, plants of Arum maculatum in flower are cut, aud 

 placed with the base in water. After removing the spathes, a few 

 spadices are fastened by means of thin rubber rings round the 

 bulb of a sensitive thermometer with a cylindrical bulb. 



* In many cases it is also advisable to keep the plants under large, not 

 perfectly air-tight cases made of zinc and glass, so as to considerably reduce 

 their transpiration. 



