WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 195 



spaces, and this means a reduction in the rate of gaseous exchange 

 and therefore in that of photosynthesis. Hence they avoid, by 

 their peculiar mode of respiration, the loss of carbon that takes 

 place in ordinary plants by the setting free of carbon dioxide into 

 the air. 



The acidity of equal-sized leaves, or pieces of leaf, chopped up 

 and extracted with water, should be tested and compared by titra- 

 tion (1) in the evening, (2) on the following morning. 



257. The intensity of respiration varies greatly in different 

 species, in different plants of the same species, in different organs 

 of the same plant, and in the same plant or organ at different 

 times. A rough comparison may be made with some form of 

 respirometer, taking the volume or weight of the plant material 

 used as a basis. Note that flowers and opening buds, like germi- 

 nating seeds, respire much more actively than fully-grown roots, 

 leaves, etc. 



258. Heat Released in Respiration. Just as the 

 dissociation of carbon dioxide in photosynthesis converts 

 kinetic energy, or energy of motion, into potential energy, 

 or energy of position, so in respiration there is a release of 

 energy that is, a conversion of potential energy into 

 kinetic energy. Some of this released energy appears in 

 the form of heat, and this may be demonstrated by 

 thermometric observations of respiring tissues, in com- 

 parison with similar but non-respiring tissues. 



(1) For experiments on the production of heat in 

 respiration we require a more or less perfect non- 

 conducting chamber, in which we place, along with the 

 seeds or other materials used, a dish or bottle containing 

 potash to absorb the carbon dioxide and thus promote 

 respiration and growth, and a thermometer as accurate 

 and sensitive as possible. In each case, also, we require 

 a control experiment similar in every way, except that the 

 plant material placed in it is killed with boiling water 

 and then placed in water containing 5 per cent, formalin, 

 or 10 per cent, corrosive sublimate, to prevent decay or 

 fermentation by micro-organisms processes in which heat 

 is released. 



The best form of non-conducting chamber is a Dewar 

 bulb consisting of two concentric bulbs with a vacuum 

 between ; or two " Thermos " or. vacuum flasks answer 



