iyo RETROSPECT. 



or the reverse may take place, and the crops of straw (of carbon) 

 may be equal, while the corn may amount to double the quantity. 

 But when we obtain twice the quantity of corn from the same 

 surface, we must have also a corresponding increase of the con- 

 stituents of the soil in the corn ; or, when we obtain twice the 

 quantity of straw, there must be twice the amount of the ingre- 

 dients of the soil in the straw. In one year the wheat may be 

 3 feet in height, and yield 1200 lbs. of seed per acre, while, in 

 another year, it may grow one foot higher, and yet yield only 

 800 lbs. 



An unequal crop indicates, under all circumstances, an une- 

 qual proportion of the constituents of the soil taken up for the 

 formation of the corn and of the straw. Straw contains and 

 requires phosphates, as well as corn, but in much smaller pro- 

 portion. 



In a wet spring, when the supply of these salts is not so great 

 as that of n!k •iies, of silica, and of sulphates, the crop of seeds 

 becomes diminished ; because a certain quantity of the phos- 

 phates, which woiJ.d otherwise be employed in the formation of 

 the seeds, is now used for the production of the stem and leases; 

 the constituents of the seeds cannot be perfected without an 

 abundant supply of phosphates. By depriving a plant of these 

 salts, we could produce artificially the state in which they attain 

 a height of three feet, and blossom without the production of 

 seeds. The crop of corn growing on a soil rich in the consti- 

 tuents of straw (a fat soil), is often less in a wet spring than upon 

 a soil poor in these ingredients (a thin soil), because the supply 

 of mineral food on the latter is greater in the same time, and is 

 in better proportion for the growth of all the constituents of plants 

 than in the former case. 



On the supposition that all the conditions necessary to our cul- 

 tivated plants, for the assimilation of food from the atmosphere, 

 existed in the most favorable form, yet the action of humus would 

 be useful in effecting a more rapid growth of the plants, and 

 thus gaining time, in all cases, the crop of carbon is increased 

 by means of humus ; and if the conditions be absent for the eon- 

 version of this element into other constituents, it as******^ the 



