, 34 PLANT PHYSIOLOGY 



stick in a vial among the seeds, and the space between thermometer and 

 neck is filled with cotton wool. 



Instead of ordinary thermometers, a differential thermometer, with the 

 two bulbs immersed in the two sets of tissues, is said to serve well for quali- 

 tative demonstration purposes (compare MACDOUGAL, 263, and DARWIN 

 and ACTON, 12). 



The student should now enlarge his knowledge of this sub- 

 ject of heat release, testing it for himself, if possible, in the nota- 

 ble case of the opening flower of Aroids. At this point, also, 

 he may best consider the general subject of the .comparative 

 activity of respiration in various plants, inclusive of Fungi and 

 Bacteria, and a comparison of their respiratory activity with 

 that displayed by animals. Here also should be considered 

 other possible sources of energy available to plants. 



The amount of energy released by the oxidation of a given 

 amount of carbon, from any given compound, to carbon dioxide, 

 is a perfectly definite and known quantity, and is expressed in 

 terms of heat in calories (i.e., the heat necessary to raise i g. of 

 water i C.). The student should now ascertain the number 

 of calories developed by the respiration of definite quantities 

 (grams) of starch and of glucose, and he will do well to determine 

 in these terms the energy released by plants in his' experiments 

 described earlier on page 131. He should also compare the 

 respiration energy of these substances with the combustion 

 energy of coal. 



The release of energy in respiration is the most important 

 subject with which the student has come into contact, or can 

 come into contact, during his entire course. It is the central 

 and crucial fact in respiration, the end and aim of the process, 

 that to which all the phenomena of gas exchange, etc., are merely 

 incidental. Consequently the student should now make cer- 

 tain of accurate knowledge as to its real physical nature. He 

 should gain clear ideas as to the forms of energy, their intertrans- 

 jormations and their relations to motion, how the dissociation of 

 carbon dioxide converts energy of motion into energy of position, 

 how this energy of position can be preserved through all the com- 

 binations into which the carbon may enter (the photosynthate and 



