196 



The Plant World. 



He can not use either. Feathered and fur-bearing animals lose 

 less heat by radiation, etc. than naked-skinned animals. Thev 

 maintain a body temperature independent of that of their en- 

 vironment with less cost of material, with less rapid respiration, 

 than if they were bare. The body-temperature of many ani- 

 mals, however, is not independent of the temperature of their 

 environment. In this respect they are like plants. Instances 

 are known in which the body temperature of plants and plant 

 parts rises for a time considerably above that of their environ- 

 ment; but this is only temporary. The smoothness and great 

 area of the surface of most plants in proportion to their mass 

 makes rapid radiation inevitable at low temperatures of the air, 

 and the maintenance of a body-temperature independent of the 

 environment is impossible. The "normal temperature" of 

 the higher animals is probably that at which the bodily functions 

 taken collectively, go on best. It is probably the optimum 

 temperature. Although there is doubtless an optimum tempera- 

 ture for all the bodily functions, taken collectively, of each kind 

 of plant, it is not a temperature which the plant itself can main- 

 tain. It inevitably loses too much heat. Are we then to re- 

 gard respiration in plants as a very wasteful process, or are 

 there in it, both in animals and plants, other uses than the libera- 

 tion of energy in the form of heat ? What possible uses are there ? 



When we realize that our knowledge of chemical energy is 

 entirely inadequate, that the only means most of us have of 

 forming any conception of it is furnished by the forms of me- 

 chanical energy which sometimes constitutes the measurable 

 end-product of reactions or processes, then we see at once that 

 the heat liberated in respiration and mostly lost by the organism 

 may perhaps be the end rather than the main product. A 

 simple illustration will at once suggest what I mean. When a 

 rapidlv revolving saw is driven through a piece of wood too 

 large to be used without cutting, there will be certain products, 

 material and energetic, useful and useless, desired and undesired. 

 A piece of wood of the proper proportions is the product desired, 

 neither the saw-dust (another material product) nor the heat 

 (mechanical energy) set free by the saw rapidly moving in the 

 resisting medium wood. We can measure the heat and all the 

 other products of sawing. We can also measure the material 



