20 INTRODUCTION 
secretions. Such is the origin of the cell-wall. It is 
secreted by the protoplast which it encloses. Sugar (as 
in the sugar-cane), starch (as in corn and nearly all 
plants), fats (as in Brazil nuts), and green coloring 
matter and other pigments, are among the substances 
secreted by protoplasm. 
26. Complexity of the Cell. A recent writer, after 
describing the minute details of cell-structure, states 
that, "The vital processes exhibited by a cell indicate a 
complexity of organization and a minuteness in the 
details of its mechanism which transcend our compre- 
hension and baffle the human imagination, to the same 
extent as do the immensities of the stellar universe." 
27. Value of the Cell-theory. It is hardly possible to 
overestimate the value of the cell-theory to botany, and 
to all biological science. By means of it we are led to 
see that all the vital activities of any living thing have 
their seat in the protoplasts of the individual cells. If a 
plant or an animal grows, it does so because the individual 
cells of its body multiply and grow; if it respires, it is 
because every living cell of its body respires; if a wound 
heals, it is because the adjacent cells reproduce them- 
selves and form new tissue to replace that destroyed by 
the wound; sickness results because certain cells behave 
abnormally, or perform their normal functions out of 
place; reproduction is the setting free by an organism of 
one or more of its cells, which become the starting point 
of a new individual. In fact, all that a plant or animal 
dose, physiologically speaking, is the sum total of what 
the cells that compose it do. Thus the cell-theory gives us 
a necessary, basic idea of all life-processes. 
