194 STORAGE OF FOOD AND WATER 



begin with, we know very little about the sequence of steps in 

 the formation of even hfeless proteids from simpler substances, 

 and protoplasm is supposed to be a complex aggregation of pro- 

 teids, water, and other possible compounds. When we speak 

 of life we have in mind a kind of energy manifested by the pro- 

 toplasm alone. We may conceive of this manifestation as being 

 due to a combination of certain rates, amplitudes, and paths of 

 vibrations of the protoplasmic molecules or structural units. 

 When new structural units are built from the food they would be 

 suited to the same mode of motion as the others and they would 

 presumably assume this mode because they are under the same 

 conditions as the others. If this conception were true so far 

 as it goes it offers nothing to clear up the great mystery of the 

 creation of living from lifeless matter. That, however, the 

 protoplasm has power to build its own substance by combina- 

 tions of different kinds of food and that the application of this 

 power is self-regulating, resulting sometimes in growth, at other 

 times in merely maintaining a balance between destruction and 

 construction, is satisfactorily established. 



Relation of Stored Food to Energy Supply. — The energy 

 which plants draw upon to keep the vital activities going comes 

 to them from the sun through the food. It seems that the 

 facts are about as follows: The sun's energy is used by the 

 chloroplasts to build carbohydrates. A part of this is decom- 

 posed, yielding energy for the construction of proteids from 

 carbohydrates and other substances. Other parts of the car- 

 bohydrates and some of the proteids are oxidized, or broken 

 down in other ways, yielding energy for the formation of proto- 

 plasm from proteids, etc. Some carbohydrates, proteids, and 

 a part of the protoplasm itself are broken dow^n and energy 

 is thus set free for doing whatever the protoplast as a living 

 agent has to do. 



This line of activities traces the source of its energy directly 

 back to the sun. The food, as well as the protoplasm, has 

 sun's energy stored up in it ready to be set free for doing work 

 and subject to the direction of the protoplasts. The construe- 



