should be regarded as involving an unnecessary risk of successful results. Some very interesting experiments have been reported, which were carried out by Mr. Thomas Jamieson, for the Aberdeenshire Farmers' Association, and these experiments are well worthy of notice. The course of procedure may be briefly stated as follows:-Some sand, which had been very fully cleared of fertilising matter, was used as a soil for the growth of some turnips. In one case all the ingredients necessary for the growth of the plant were added by means of a suitable artificial manure, and a perfect development took place. In a second instance the exhausted sand received a supply of the same manure, except that the phosphoric acid was in this case entirely omitted. The result was that after a short growth, and a struggle for life, the plant died. In the third trial all the materials were added except the lime, and in this case also the plant failed to make more than a feeble growth, and soon died. In the fourth trial the potash was omitted, but the plant continued to struggle slowly on, and did not die as quickly as the others. On an examination of the sand, it was found that the plant had received a small quantity of potash by the decomposition of the sand, and these insufficient supplies protracted the life of the plant, but failed to enable a perfect growth to be attained. The lessons taught by these simple but very interesting experiments, tend to show the importance of plant-food being perfect and complete. The

addition of a very minute quantity of iron to the plant-food has already been mentioned as being capable of materially altering the character of that food. Plants which had previously made only a sickly growth, because of the absence of iron, quickly put on a rich green and luxuriant appearance, as soon as the needed supply was added. The same influence has been observed in cases where other materials were absent, and hence it is that in practice it is necessary to have the plant-food capable of meeting the full demands of vegetation, if the cultivator of the soil would secure a successful result from his operations.

CHAPTER XXI.

ONE of the natural results arising from plants requiring a supply of all the materials they need for their growth, is that that portion of the food which is least abundantly supplied determines the fertility of the land. If, for example, phosphoric acid were to be absent, and every other portion of the plant-food should be present, that land must be a barren soil for any and every crop requiring phosphoric acid. It would be immaterial how abundant every other necessary may be; here is a want which has not been provided for, and this deficiency renders that land barren. Hence the truth, which cannot be too frequently enforced upon the attention of farmers,

that the least abundant portion of the plant-food determines the measure of fertility. It is no use supplying that which does not provide for the deficiency. There is a want of some essential for growth, and until this is supplied successful cultivation cannot take place. You give a mason stones and

mortar to build a wall; at length he calls for more mortar, and you send him more stones; he builds as far as his mortar will permit, and finally he stops his work. The plant, by its sickly appearance and feeble growth, tells, as plainly as it can, that it wants something. In too many cases farmers purchase what is not wanted, and fail to supply what is needed. Little or no good results, and the manure-dealer has the credit of sending a bad manure, whereas the truth is the farmer has not supplied the deficiency. He may have used some good fertilising matter, but it has not been suitable for his requirements, and hence it has not increased the productive powers of the soil.

The natural supply of plant-food which needs our special care is in the soil; and as we have seen what our various crops require, it will now be desirable to see how these requirements are provided for. Soils differ very greatly in their composition, but we find that all fertile soils contain all the substances which our cultivated crops require. It is unnecessary to repeat the long list of substances already given as the "bill of fare" required by our cultivated crops; it will be enough for our present purposes to say that there is to be found in all fertile soils a sufficient

supply of each and every material. A moment's reflection will show that such must be the fact, for if there were a deficiency of any one of the needed supplies, the soil would not be fertile and productive. So it is also with other intermediate qualities of soils. We say that such and such a soil is but moderately productive, and this may arise from some portion of the plant-food being present, but not in a full and sufficient quantity. There are cases in which other agencies than plant-food exert an influence in determining the result. Of this class, it is here only necessary to mention the presence of injurious matter, imperfect tillage, or a bad climate. But, limiting our remarks for the moment to the influence of plant-food, it may be stated that a more or less perfect and complete supply of plantfood in a well-cultivated soil, renders that soil more or less fertile, and in a degree proportioned to the completeness and abundance of the supply.

Numerous cases are familiar to us, especially in the United States, of new lands being reclaimed, brought into cultivation for the first time by man's industry; and yet, after a few years of imperfect corntillage, that land has ceased to be profitable for the growth of corn. The result has been a gradual retirement to new soils, which are ultimately given up for the same reason. This failure in the growth of paying crops does not arise from an entire exhaustion of the plant-food in these soils, but rather from the fact that a partial exhaustion has rendered the supply imperfect and the cultivation unpro

fitable. As and when circumstances render it desirable for the cultivation of such lands to be renewed, the existing deficiencies will be supplied, and the land will be restored to a productive condition. This will be most economically effected by supplying the materials which are especially deficient, rather than by any attempt to replace the entire supply, previously used up by the growth of corn crops. It is the weak links in the chain which will need to be strengthened, rather than that a new chain will have to be made.

One other important ingredient in plant-food remains to be referred to, and that is the nitrogen which plants require. At present we gain less guidance from the analysis of our crops, than from the evidence obtainable from the experiments which have been carried out upon the living plants. By analysis we obtain the clearest possible proof, that all our cultivated plants require a supply of nitrogenous matter in their food; and hence we know that it is as great a necessity for the successful cultivation of our crops, as any one of the constituents of plant-food already noticed. There is, however, a great variety of forms in which nitrogen may be added to the soil; and it is in reference to the action of these several nitrogen compounds that the actual experience of the farmer at present gives the safest guidance for its use. Under a good system of husbandry the soil is enriched in its stores of nitrogenous matter by the absorption of ammonia from the atmosphere, and by the accumulation of vegetable matter in the soil