12 Plant Life and Evolution 



from CO 2 and water of simple organic com- 

 pounds. 



The ability to feed entirely upon inorganic matter 

 is not, however, in all cases dependent upon light. 

 We have already seen that certain bacteria can do 

 this in the absence of light, probably through the 

 agency of some form of chemical energy. Animals, 

 so far as we know, are absolutely dependent upon 

 organic food for their existence, feeding directly 

 or indirectly upon plants. Where chlorophyll is 

 present in animals, as for instance in the green 

 hydra and fresh-water sponges, it has been shown 

 that the green color is due to the presence of minute 

 green algae which live within the tissues of their 

 host. Of unicellular animals, it has been claimed 

 that a species of Vorticella contains chlorophyll, and 

 a common flagellate organism Euglena, which is 

 structurally more like an animal than a plant, and 

 is often considered to be a true animal, contains 

 abundant chlorophyll and is undoubtedly capable of 

 photosynthesis. 



Plants the Manufacturers of Organic Matter. 

 Plants being the manufacturers of all organic food, 

 their importance in the economy of nature is at 

 once evident. Without them all animal life would 

 necessarily soon cease. While the green plants take 

 the first place in the manufacture of organic com- 

 pounds, it must be remembered that the lowest of 

 all plants, the bacteria, are also indispensable in 

 maintaining the circulation of materials necessary 



