58 



ECOLOGY 



In sunlight a green water plant 

 gave off bubbles (of oxygen). 



Part II 



Mouse could breathe 



in closed jar. (Oxygen 



supplied by plant ) 



PRIESTLEY'S DISCOVERY 



Fig. 4.6. The chemist (England, 1733-1804), Joseph Priestley kept a plant grow- 

 ing within a glass jar connected with another jar in which he kept a mouse. The 

 mouse breathed on comfortably because the plant provided it with oxygen, a 

 product of its photosynthesis. (Data for figure from Memoirs of Joseph Priestley, 

 1:253. London, J. Johnson, 1806.) 



and activates the photosynthesis of green plants. Thus the sun surrounds plants 

 with light and keeps air and water circulating about them. Plants may have 

 all of this without going after it as the majority of animals do. Light bathes 

 the whole plant from above or from one or more directions; the branches 

 reach out for light and the leaves take positions to receive it. Light does not 

 penetrate deeply into the tissues, but leaf surfaces are spread out and the 

 chlorophyll is always near to them (Fig. 4.8). The spread of maple leaves to 

 receive light is a marvel of efficient arrangement. The essentials for a green 

 plant's existence are in two layers of its environment. Light and air are above; 

 there the plant is green and its stem upstanding. Water and minerals are be- 

 lov/; there the plant is colorless and its roots are pliant. 



The Individual. The plant has a particular form recognizable as character- 



