Intermediate Organisms 187 



plasm, and the chlorophyl, which is simply the green pigment contained 

 in the chloroplast. 



Photosynthesis. 



In the final analysis, every particle of food, which an animal eats, 

 must come from and through the plant world. For example, when one 

 eats a piece of steak, the animal from which it was taken, lived either 

 directly on plants or on other animals which fed on plant-life. 



Here it is well to appreciate the interesting way nature has of 

 keeping a sort of balanced quantity of all needed organisms ; for the 

 meat-eating animals or carnivores do not allow an overproduction of 

 plant-eating animals or herbivores, and are prevented from multiplying 

 too rapidly by parasites in their own ranks ; while much of the vegetable 

 world is saved because animals eat each other. 



Consideration of these facts has led to the statement that the 

 important thing in life is to get enough to eat and to prevent one's self 

 from being eaten. 



The plants manufacture their own food from the substances they 

 can extract from the surrounding soil and the air. Plants are, therefore, 

 not dependent upon other animals or plants for their food as animals 

 are. Those organisms, dependent upon other living organisms for their 

 food, are said to be heterotrophic ( ) in nutrition, 



while those, which can manufacture their own food, are said to be 

 autotrophic ( ) in nutrition. 



But only those plants, which possess chlorophyl, are autotrophic. 

 Therefore, fungi, molds, and most bacteria, which are plants, but which 

 have no chlorophyl, are heterotrophic; and, being obliged to live upon 

 other organisms, they are parasitic ( ) or 



saprophytic ( ). 



Chlorophyl is either contained in a chloroplast, as already stated, 

 or, it is scattered throughout the protoplasm in the simpler green plants. 

 Chemically, chlorophyl is a complex compound of carbon, hydrogen, 

 oxygen, nitrogen, and magnesium ; its probable empirical formula is 

 given by one investigator as C 54 H 72 6 N 4 Mg. Iron, while not a con- 

 stituent of chlorophyl, is, nevertheless, always present in the chloroplast 

 and seems to be essential to chlorophyl formation. Either in solution 

 or in the living plant, chlorophyl absorbs part of the light which falls 

 upon it. The energy of the light thus absorbed by the chloroplast is the 

 active agent which enables the plant to perform its work. As light is 

 required, this process goes on only during the day. 



The materials from which carbohydrate food is manufactured by 

 green plants are carbon dioxide and water. Carbon dioxide is present 

 in the atmosphere in the small but constant concentration of about 3 

 parts per 10,000 parts of air, and, therefore, readily available to such 

 plants as Pleurococcus. "Water is absorbed directly from the sub- 

 stratum through the cell wall into the protoplast. The carbon dioxide 



