To what is this difference owing? Is it to the nature of the soil, or does it depend upon the _variety_ of wheat experimented upon? It seems to depend partly upon both. Thus, on the same field, in Ravensworth dale, Yorkshire, on a rich clay soil abounding in lime, the _Golden Kent_ and _Flanders Red_ wheats were sown in the spring of 1841. The former gave an excellent crop, while the latter was a total failure, the ear containing 20 or 30 grains only of poor wheat. The straw of the former left 165 lbs. of ash from 1000 lbs., that of the latter only 120 lbs. Something, therefore, depends upon the variety. But as from the straw of a good wheat crop grown near Durham this last summer on a clay loam I obtained only 66 lbs. of ash, I am persuaded that the very wide variations in the quantity of ash left, by different wheat straws, must be dependent in some considerable degree upon the soil. The truth, so far as it can as yet be made out, seems to be this—that every plant must have a certain quantity of inorganic matter to make it grow in the most healthy manner;—that it is capable of living, growing, and even ripening seed with very much less than this quantity;—but that those soils will produce the most perfect plants which can best supply all their wants,—and that the best seed will be raised in those districts where the soil, without being too rich or rank, yet can yield both organic and inorganic food in such proportions as to maintain the corn plants in their most healthy condition. SECTION III.—OF THE QUALITY OF THE ASH OF PLANTS. But much also depends upon the _quality_ as well as upon the _quantity_ of the ash. Plants may leave the same weight of ash when burned, and yet the nature of the two specimens of ash, the kind of matter of which they respectively consist, may be very different. The ash of one may contain much lime, of another much potash, of a third much soda, while in a fourth much silica may be present. Thus 100 lbs. of the ash of _bean_ straw contain 53½ lbs. of potash, while that of _barley_ straw contains only 3½ lbs. in the hundred; and, on the other hand, the same weight of the ash of the latter contains 73½ lbs. of silica, while in that of the former there are only 7½ lbs. The quality of the ash seems to vary with the same conditions by which its quantity is affected. Thus— 1. It varies with the kind of plant. 100 lbs. of the ash of wheat, barley, and oats, for example, contain, respectively, Wheat. Barley. Oats.