UNITY OF LIFE 261 



still more kinds of cells, also act as units. There is some 

 relation between the activity of the roots and the activity of 

 the leaves ; there is a very definite relation between the activity 

 of the hand that conveys food and the activity of the mouth 

 that receives it ; and also between the behavior of the digestive 

 system and the behavior of the conducting system. 



Incidentally, organisms commonly take in, besides the usable 

 material, material that is not usable. The elimination of this 

 refuse is accomplished very simply by the ameba ; the animal 

 simply moves away from the refuse, leaving it behind. In the 

 daisy the excess of mineral matter received from the soil is 

 usually deposited in the form of insoluble compounds in 

 various parts of the root or stem or leaf. In the human body 

 the refuse from the food material is accumulated for a period 

 and then discharged by the coordinated activity of special 

 nerves and muscles. 



314. Energesis and respiration. In the one-celled animal 

 there is energesis, depending upon the chemical union of 

 oxygen with other substances, under the influence of certain 

 ferments. This is also true of the daisy and of the human 

 body. 



In the daisy, respiration is necessary for every cell ; and so 

 it is with man. But not all the cells of these organisms can 

 get their oxygen directly from the outside, nor can they all 

 discharge their carbon dioxid directly to the outside. In the 

 daisy the root cells absorb oxygen by osmosis, the oxygen pass- 

 ing directly into the epidermal cells, and from these by osmosis 

 into the deeper layers of cell. Carbon dioxid diffuses out by 

 osmosis in a similar manner. The cells of the leaf and of the 

 stem lying under the skin absorb oxygen from the air sur- 

 rounding them in the intercellular spaces ; and from these 

 spaces there are connections to the outside atmosphere by way 

 of the little breathing pores, or stomates. The gases move in 

 and out through these open spaces and passages, controlled 

 entirely by the changing osmotic pressure, 



