BERGSON' S ORGANIC EVOLUTION 165 



method of deriving potential energy from plant reservoirs it likewise 

 stores up potential energy for itself by the direct action of the sun's 

 rays on its chlorophyll. But in the course of higher development it 

 was found that these two functions, that of storing up energy and its 

 expenditure in free movements, were incompatible in the same or- 

 ganism. There thus opened out before the organism two lines of 

 development, one of greater movement, but with all the hazard of an 

 uncertain food supply, the other of fixity, but with a certainty of food 

 supply; the former resulted in the animal kingdom, the latter in the 

 vegetable. 



Since, however, these two kingdoms are branches of the same life im- 

 petus each contains something of the other. The difference lies merely 

 in the tendencies upon which each lays emphasis, while it leaves the 

 other tendencies lying dormant. So that plants and animals can not be 

 defined by mutually exclusive characters, but rather by the accentuation 

 of certain tendencies. Plants take their food as a rule from the inor- 

 ganic, animals from the organic ; as a result plants are usually fastened 

 to the earth, immobile ; animals get their food through movement. As a 

 consequence of this differing method of food getting the plant cell 

 surrounds itself with a hard coat of cellulose through which external 

 stimuli can with difficulty affect the organism, and there is hence made 

 possible but a very slight consciousness. Since to the animal cell 

 movement is essential to food getting, it can not completely encase itself 

 in a hard external skeleton ; it thus follows that external stimuli readily 

 affect the organism and there is hence rapidly developed an ever higher 

 type of consciousness. 



Consciousness, as used by Bergson, is not limited to self-conscious- 

 ness, but is the kind of consciousness that Jennings in his " Behavior 

 of Lower Organisms " is inclined to believe is possessed by all animals 

 from the highest to the lowest. Bergson relates it to mobility. " The 

 humblest organism is conscious in proportion to its power to move 

 freely." 



The elements into which a tendency splits do not possess the same 

 power to evolve. The truly elementary tendencies continue to evolve, 

 leaving behind the residual, split-off tendencies. This is illustrated 

 in the development of the plant kiDgdom, where it is the carbon-fixers 

 which carry on the main line of evolution. 



Along the animal pathway, three of the main branches are those of 

 the mollusks, arthropods and vertebrates. During the middle Paleozoic 

 all had run into the blind alleys of stagnancy, of torpor, since most 

 forms of these phyla had become enclosed in a hard external skeleton; 

 but before this condition had become universal, some of the arthropods 

 assumed, instead of the hard external skeleton of the crustacean, the 

 soft one of the insect, and among the vertebrates the armored fish gave 

 place to the unarmored. 



