The direct source of the nitrogen contained in plants is an unsolved mystery, though the ultimate source of much of it must be the atmosphere. A wheat crop gave on unmanured land from 15.9 to 25.2 pounds of nitrogen, per acre, yearly, but the amount found in the rainwater of the same district was only from 6.23 to 8.58 pounds per acre. Singular to say, the use of a fertilizer, called a "complex mineral manure" in the reports, added only about two pounds of nitrogen per acre. But the case is altered when potassic manure is used, and especially when applied to land bearing beans. Such a crop gains 13-1/2 pounds of nitrogen by the addition of saltpetre, or 28 per cent. A similar result was obtained with clover--a leguminous crop. A potassic fertilizer increased the yield of nitrogen one-third. One of the anomalies observed in the study of plant growth is that a good crop instead of exhausting the soil seems to improve it. The better the crop, and the more nitrogen removed, the better will the succeeding crop be. Thus clover removes a much larger amount of nitrogen than wheat, the quantity being on unmanured land, say 30.5 pounds per acre for clover and 20.7 pounds for wheat, and yet the wheat crop is improved if clover is occasionally interpolated or a fair rotation of crops kept up. In 1874 barley succeeding barley gave 39.1 pounds of nitrogen, while barley following clover gave 69.4 pounds of nitrogen withdrawn from an acre of soil. These amounts take no account of the nitrogen carried off by the drainage of the soil, which analysis of drainwater proves to be considerable. The source of all this nitrogen is undoubtedly the atmosphere, but the mode of conveying it into the soil is unknown. IMPORTANT PREHISTORIC DISCOVERIES. Few persons are aware of the wealth of what are called "prehistoric" remains. The finding of an isolated skeleton, in a cave, with stalagmite completely covering it, is accepted as an occurrence that is not very remarkable. However ancient it may be, the preservation of the bones is exceptional. But a late discovery in France, near Hastiére-sur-Meuse, is of much more importance. No less than fifteen burial caverns were found, and from the five that have been explored no less than fifty-five human skeletons have been taken, among which are thirty-five well-preserved skulls. In addition to these "finds" the plateaux yielded sixteen dwelling places of the old inhabitants from which have been taken a quantity of stone implements. These show the age of the skeletons to be that of the polished, or "new" stone period. The prospect of being able to restore the men who lived before the earliest recorded dates is now very good. Some hundreds of their skeletons, with a valuable series of skulls and enormous collections of their handiworks, are now in the museums of the world.