=Trees as Land Formers.=--John Gifford, in a paper presented to the Franklin Institute on Forestry in Relation to Physical Geography and Engineering, mentions as illustrating the way forests counteract certain destructive forces, the mangrove tree as "the great land former which, supplementing the work of the coral polyp, has added to the warm seashore regions of the globe immense areas of land." The trees grow in salt water several feet deep, where their labyrinth of roots and branches collect and hold sediment and flotage. Thus the shore line advances. The seeds, germinating on the plant, the plantlets fall into the water, float away till their roots touch the bottom, and there form the nucleus of new islands and life. The forest constantly improves the soil, provided the latter is not removed or allowed to burn. The roots of trees penetrate to its deeper layers and absorb great quantities of mineral matters, a large percentage of which goes to the leaves, and is ultimately deposited on the surface. "The surface soil is both enriched by these mineral substances and protected by a mulch of humus in varying stages of decomposition. As the lower layers rot, new layers of leaves and twigs are being constantly deposited, so that the forest soil, in the course of time, fairly reeks with nourishing plant food, which seeps out more or less to enrich neighboring soils." The forest is also a soil former. "Even the most tender rootlet, because of its acidity, is able to dissolve its way through certain kinds of rock. This, together with the acids formed in the decomposition of humus, is a potent and speedy agent in the production of soil. The roots of many species of trees have no difficulty whatever in penetrating limestone and in disintegrating rocks of the granitic series. As the rock crumbles, solid inorganic materials are released, which enrich neighboring soils, especially those of the valleys in regions where the forest is relegated to the mountain sides and top, as should be the case in all mountainous regions. In view of the destruction caused by mankind, it is a consoling fact that Nature, although slowly, is gradually improving her waste lands. If not interrupted, the barest rock and the fallowest field, under conditions which may be called unfavorable, will become, in course of time, forest-clad and fertile. The most important function of the forest in relation to the soil, however, is in holding it in place and protecting it from the erosive action of wind and rain."