8o The Living Plant 



work is accomplished. Energy is most familiar as heat or elec- 

 tricity, though manifest also in light and in chemical reactions. 

 Without energy there is no motion, no power, no work; and with- 

 out it a plant or an animal stops as dead as an engine when no fire 

 burns under its boiler. Plant work, therefore, requires and im- 

 plies a supply of energy. And with this conclusion it will be well 

 to gather the foregoing matters into a generalization, another 

 of our botanical verities; all plants, like all animals, are inces- 

 santly at work while alive, as truly as any moving machine, not only in 

 the performance of their active and visible movements, but also in the 

 bare maintenance of their existence; and this work requires a pro~ 

 portional supply of energy. 



It is now our business to find the source of the energy by which 

 plants do their work. We know the source of the energy in the 

 work of the engine just mentioned; it is the heat released from 

 the burning of coal in a grate. But what is the source of the energy 

 in the work of the plant, which has neither grates, nor boilers, 

 nor flaming of fuel? 



When the student of science is faced by a problem like this, 

 his first resource is to look around for suggestions from some 

 analogous process. In this instance he would turn naturally 

 to animals, and his earlier studies on the physiology of man would . 

 have taught him that the power of animals to do work is connected 

 in some way with their respiration, that process in which they 

 give forth the gases carbon dioxide and water vapor to the air, 

 while absorbing the gas oxygen into their bodies. How inti- 

 mately this process is connected with work is easily realized 

 when we recall the familiar fact that respiration increases in pro- 

 portion as work becomes harder. Is it possible, then, that 

 plants also respire? That is, do plants in their work release car- 

 bon dioxide, and absorb oxygen? Obviously this matter is de- 

 terminable by experiment, and the following is a very good 

 method. In a bottle arranged as shown by the picture (figure 

 27), we place some plant parts which are actively working with- 



