18 HOW CROPS FEED. 
When a seed germinates in a medium that is totally 
destitute of one or all the essential elements of the plant, 
the embryo attains a certain development from the mate- 
rials of the seed itself (cotyledons or endosperm,) but 
shortly after these are consumed, the p'antlet ceases to in- 
crease in dry weight,* and dies, or only grows at its own 
expense. 
A similar seed deposited in ordinary soil, watered with 
rain or spring water and freely exposed to the atmosphere, 
evolves a seedling which survives the exhaustion of the 
cotyledons, and continues without cessation to grow, 
forming cellulose, oil, starch, and albumin, increases many 
times—a hundred or two hundred fuld—in weight, runs 
normally through all the stages of vegetation, blossoms, 
and yields a dozen or a hundred new seeds, each as perfect 
as the original. 
It is thus obvious that Air, Water, and Soil, are capa- 
ble of feeding plants, and, under purely natural conditions, 
do exclusively nourish all vegetation. 
In the soil, atmosphere, and water, can be found no 
trace of the peculiar organic principles of plants. We 
look there in vain for cellulose, starch, dextrin, oil, or al- 
bumin. The natural sources of the food of crops consist 
of various salts and gases which contain the ultimate ele- 
ments of vegetation, but which require to be collected and 
worked over by the plant. 
The embryo of the germinating seed, like the bud of a 
tree when aroused by the spring warmth from a dormant 
state, or like the sprout of a potato tuber, enlarges at the 
expense of previously organized matters, supplied to it 
by the contiguous parts. 
As soon as the plantlet is weaned from the stores of the 
* Since vegetable matter may contain a variable amount of water, either that 
which belongs to the sap of the fresh plant. or that which is hygroscopically re- 
tained in the pores, all comparisons must be made on the @ry, i. e., watersree 
substance, See ** How Crops Grow,” pp. 53-5, 
