I have used Guano frequently, and, though it has generally made its mark, I never yet felt sure that it returned me a profit over its cost. Phosphates have done better, especially where applied to Corn in the hill, either at the time of planting or later; yet my strong impression is that Flour of Bone, applied broadcast and freely, especially when Wheat or Oats are sown on a field that is to be laid down to Grass, pays better and more surely than anything else I order from the City, Gypsum, and possibly Oyster-Shell Lime, excepted. My experience can be no safe guide for others, since it is not proved that the anterior condition and needs of their soils are precisely like those of mine. I apprehend that Guano has not had a fair trial on my place--that carelessness in pulverizing or in application has caused it to "waste its sweetness on the desert air," or that a drouth following its application has prevented the due development of its virtues. And still my impression that Guano is the brandy of vegetation, supplying to plants stimulus rather than nutrition, is so clear and strong that it may not easily be effaced. It seems to me plainly absurd to send ten thousand miles for this stimulant, when this or any other great city annually poisons its own atmosphere and the adjacent waters with excretions which are of very similar character and value, and which Science and Capital might combine to utilize at less than half the cost of like elements in the form of Guano. My object in this paper is to incite experiment and careful observation. No farmer should absolutely trust aught but his own senses. A Rhode Islander once assured me that he applied to four acres of thin, slaty gravel one hundred pounds per acre of Nitrate of Soda which cost him $4 per hundred, and obtained therefrom four additional tuns of good Hay, worth $15 per tun: Net profit (after allowing for the cost of making the Hay), say $30. He might not be so fortunate on a second trial, and there may not be another four acres of the earth's surface where Nitrate of Soda would do so well; but, should I ever have a fair opportunity, I mean to see what a little of that Nitrate will do for _me_. And I hope farmers may more and more be induced to conform in practice to the Apostolic precept, "Prove all things: Hold fast that which is good." No one's success or failure in a particular instance should be conclusive with others, because of the infinite diversity of antecedent and attendant circumstances; but if every thrifty farmer would give to each of the commercial fertilizers--Lime, Gypsum, Guano, Raw Bone, Phosphates, Ashes, Salt, Marl, etc.--such a careful trial as he might, observing closely and recording carefully the results, we should soon have a mass of facts and results, wherefrom deductions might be drawn of signal practical value to the present and to future generations.