CHAPTER V. 
THE MICROSCOPY OF THE COMMON STARCHES. 
1. Origin and Nature of Starch.—All living things 
depend for existence upon the potential energy of organic 
compounds which they take in as foods and break down 
to simpler substances; and to make good this constant 
drain upon the limited stock of organic matter in the 
world there is only one source of supply, the chlorophyll 
bodies of green plants. Here rays of sunlight are absorbed, 
and by the'r energy carbon dioxid and water are united 
to form starch, oxygen being set free; the kinetic energy 
of the sun is thus transformed and stored up in potential 
form. Ultimately the whole structure of organic life 
depends on this process, as the universe, of mythology, 
rested upon the back of the fabled tortoise. 
Starch is an insoluble carbohydrate substance belong- 
ing to the cellulose group and having probably the formula 
(C,H, O;)x. It occurs as a white powder made up of 
small grains a few hundredths, or rarely a tenth, of a milli- 
meter in diameter, of a shape varying with the plant by 
which it is formed, but more or less characteristic for 
each species. The grains are in general built up of con- 
centric layers, the outer one resembling cellulose, while 
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