18 HOW CROPS FKED. 



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 cei'tain development from the mate- 

 rials of the seed itself (cotyledons or endosperm,) hut 

 shortly after these are consumed, the plantlet ceases to in- 

 crease in dry weight,* and dies, or only grows at its own 

 expense. 



A similar seed deposited in ordinary soil, Avatered 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 fold— in weight, nms 

 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 cai)a- 

 ble of feeding plants, and, under purely natural conditions, 

 do exclusively nourisli 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 celhilose, 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 n- 

 lained in the pores, all comparisons must be made on the dry, i. e., water-fret 

 iubstaqce. See "How Crops Grow," pp. 53-5. 



