CHAPTER IV 

 METABOLISM OF GREEN PLANTS 



Matter and force are the two names of the one Artist who 

 fashions the living as well as the lifeless. Huxley. 



IT has been emphasized that life is only known to us in the 

 form of individuals, and we turn now to concrete examples 

 of unicellular plants and animals which present, in relatively 

 simple form within the confines of a cell, an epitome of all the 

 fundamental life processes which .we shall later have occasion 

 to review in their complex expressions in the higher animals 

 and plants. 



Unicellular green plants are distributed all over the world 

 and adapted to a great variety of conditions. We find them, 

 for example, forming green coatings on the bark of trees, 

 scums on puddles and ponds, or being blown about as dust 

 by winds. Of the many hundreds of species we select 

 Sphaerella lacustris because it can readily be obtained and 

 kept for observation, and because its life history has been 

 carefully studied. 



A. STRUCTURE AND LIFE HISTORY OF SPHAERELLA 



A single Sphaerella is invisible or barely visible to the naked 

 eye, but, like many another microscopic form, it makes up in 

 numbers for the small size of the individual, and sometimes 

 gives a stagnant pool of rain-water a bright green or red 

 color. Sphaerella has a complicated LIFE CYCLE, or series of 

 forms which it assumes under different conditions, chiefly 

 environmental. We shall take as the initial stage for descrip- 



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