However valuable this fortified guano may be--and it is, undoubtedly, a most valuable manure--its action cannot be supposed to be exactly similar to the old Peruvian guano, which it resembles in the percentage of its nitrogen, phosphates, and potash. Much of the distinctive value of guano as a manure, as will be pointed out immediately, lies in the fact that it contains its manurial ingredients in a variety of differently soluble compounds, which are gradually rendered available in the soil for the plant's needs. This undoubtedly is one of the reasons why the action of guano among manures is quite unique; and there are other reasons which we probably do not clearly understand. However skilfully the composition of the guano may be artificially simulated, it still remains an undoubted fact that the "equalised" guano is not exactly similar in its action to the genuine article. Nevertheless, that it is superior in its results to the poorer classes of guano at present available, and to ordinary compound manures, there can be little doubt. A great merit of the equalised guano is, however, that it is sold at a lower price than guano as imported; and as the guano is sold on a guaranteed analysis, the practice has done much to advance the true interests of agriculture. _Its Action as a Manure._ Next to farmyard manure, guano may be regarded as the most "general" of all the commonly used manures; for in addition to nitrogen, phosphoric acid, and potash, it contains nearly all the other plant ingredients, such as lime, magnesia, &c. Its special value as a manure, however, does not merely consist in the amount of valuable plant-food it contains. Like farmyard manure, it owes much of its characteristic action to the state of the intimate mixture of its manurial constituents, and also, as has already been pointed out, to the fact that it contains those constituents in a great variety of chemical forms, each of which differs in its solubility, and consequently availability for the plant's needs. Take, for example, the great number of different forms of nitrogen it contains. Some are in the condition in which plants can immediately absorb them, while the rest are in a series of less and less available forms, which, however, are gradually converted into available forms as the plant requires them. Like farmyard manure, again, it may be applied with almost equally good results to all kinds of crops and on all kinds of soils. We have in guano, in short, an admirable example of the value of applying our manurial ingredients in different forms. That this is no mere theory is abundantly proved by the large number of different experiments which have in the past been carried out with guano, more especially the well-known experiments made by Grouven, the German chemist. In those well-known experiments, guano was tested against a large variety of different fertilisers, and the tests were so arranged