Page:Popular Science Monthly Volume 28.djvu/700

682 shallow ground it produces more but of less valuable quality. Two needles in one sheath characterize this species. The heart-wood of this pine contains 5·7 per cent of resin, the sap-wood proportionately less.

The sap-wood of this tree is quickly destroyed when the tree is cut; it assumes a dark-blue color and rots, through the agency of the mycelium of a fungus called Ceratostoma piliferum.

This tree is at present the most valuable and most cultivated timber-tree of Northern Germany.

The white pine, or common American pine (Pinus strobus), is now also extensively cultivated in Germany, where some forests can be found of trees about a hundred years old. Its wood has the lowest specific gravity of all coniferous wood. In spring, on account of the thinness of its bark, the tree is quickly warmed through, and the wood cells, formed in the beginning of the spring, are thin-walled; at the close of the period of vegetation in summer, the annual rings are finished by a few thick-walled narrow cells, thus giving only little thickness to the hard part of the annual layer. In amount of resin this pine stands at the head of all conifers, containing 6·9 per cent. The percentage increases up to the age of one hundred years, and with it the quality of the wood. It is of little value when young and exposed to moisture. Pinus cembra, a native of the Alps and Siberia, forms only small, dense rings every year during the short summers of these regions; the wood hence becomes heavier, and, although less resinous, more valuable.

A very valuable tree of Europe is the larch (Larix Europæa), which is native only in the colder regions of Europe and Asia; its wood consists of narrow annual rings, grown during the short summers of those countries. In the percentage of resin it stands between Pinus and Picea; its wood is more reddish, like that of the genus Pinus, and its resiniferous ducts are constructed like those of Picea; it contains 3·9 per cent of resin.

Just now, the different German governments are experimenting with the introduction of American trees which, it is expected, will stand the climate and furnish better wood, or, in proportion, a larger quantity, than the German forest-trees now cultivated. One of those of which much is expected is the Douglas spruce (Pseudotsuga Douglasii). Mr. J. Booth, of Hamburg, has cultivated this tree for a long time, and has already some very fine specimens in his park. I was enabled through his kindness to examine its wood carefully; the specific weight is very much above that of European conifers of the Pinus genus, but not as high as that of the larch; its quality increases in proportion to the width of its layers—a fact which, until a short time ago, was considered directly contrary to what is the case with wood from European pines.

Professor Sargeant, of Cambridge, has made the contribution to