132 PLANT PHYSIOLOGY 



subject, in part through the literature and in part through aid 

 of the following: 



Suggested Experiments. With the respirometer determine the respi- 

 ratory ratio of tissues other than seeds, viz., (a) opening flower-buds, (6) 

 growing terminal buds, (c) young growing leaves, (d) young roots, (e) some 

 succulent shoots of Cacti or Euphorbias, (/) other available living tissues. 

 The instrument must of course be kept in darkness, and all injury to the 

 tissues must be minimized. 



Again, with the respirometer determine the respiratory ratio in other 

 kinds. of seeds, such as Flax, Peas, Radish. 



In using the respirometer for this purpose, it is obviously indispensable 

 to provide for a possible movement of the index liquid in either direction; 

 hence the reagent in the measuring-tube must be started at a point whence 

 it may range down as well as up.. 



In this connection the student should inform himself upon 

 our knowledge of the meaning of the various respiratory ratios, 

 and of the products of imperfect and oj excessive oxidation, and 

 with the possible ecological significance thereof. Along with this 

 subject he should also make certain that he understands clearly 

 the mutual relationships of respiration and photosynthesis in 

 green tissues, their coexistence there, their relative amounts under 

 different conditions of light and temperature, their possible utiliza- 

 tion of one another's products, and the conditions both of light and 

 of temperature under which they may exactly balance one another. 



There yet remains one other marked feature of photosyn- 

 thesis for the reciprocal of which we should now seek in respira- 

 tion, namely, the absorption or storage (conversion of kinetic 

 to potential) of energy; and the question arises whether any 

 energy is released (converted from potential to kinetic) in respira- 

 tion. Familiar facts connected with the process in the animal 

 kingdom {viz., the greater activity of respiration, as shown by 

 the breathing, accompanying greater exertion) imply that this 

 is so, but it is difficult to test directly in plants. There is, 

 however, one fact about the transformations of energy in gen- 

 eral which may be utilized for a test of this question, namely, 

 no matter in what form energy is released, some of it always 

 appears as heat. Our inquiry then resolves itself into this: 



Is any heat released in the respiration of plants? 



