SECT. II 



PHYSIOLOGY 



221 



seeds (Peas), if examined in large quantities, show under proper 

 conditions a rise in temperature of 2° C. The greatest spontaneous 

 evolution of heat manifested by plants has been observed in the 

 inflorescence of the Jraceae, in which the temperature was increased by 

 energetic respiration 10°, 15°, and even 20° C. Also in the large 

 flower of the Victoria regia temperature variations of 15° C. have been 

 shown to be due to respiration. One gramme of the spadix substance 

 of an Jraceae exhales, in one hour, up to 30 cubic centimetres C0 2 ; 



Fig. 192. — Experiment to show the direct communication of the external atmosphere with the 

 internal tissues of plants. The glass tube R, and the leaf P, are fitted air-tight in the bottle G ; 

 upon withdrawal of the air in the bottle by suction on the tube R, the external air penetrates 

 the intercellular spaces of the leaf, through the stomata, and escapes in the form of small 

 air-bubbles from the cut surface of the leaf-petiole. (From Detmer's Physiol. Pract.) 



and half of the dry substance (the reserved sugar and starch) may be 

 consumed in a few hours as the result of such vigorous respirations. 



That other processes, in addition to respiration, co-operate in the production 

 of heat is apparent from the fact that the amount of heat evolved does not vary 

 proportionally to the carbonic acid exhaled. The high temperature (up to 70° C. ) 

 observable in germinating Barley does not result from respiration alone, but is due 

 to the decomposing activity of a Fungus. 



The Movement of Gases within the Plant. — The entrance of 



