Not all the streams of the Park were originally stocked with fish. Where the waters leave the great volcanic plateau and fall to the underlying formations, the cataracts form impassable barriers to the ascent of fish. In the lower courses of all the streams there were native trout, but above the falls, with one exception, there were none. The exception of the Yellowstone River and Lake is a most interesting one. Why the Falls of the Yellowstone, the highest and most impassable of all, should apparently have proven no barrier, is at first a puzzling question. But the solution is to be found in Two-Ocean Pass. Across this remarkable divide fish may easily make their way, and the Yellowstone Lake is unquestionably stocked from this direction. We thus have an example, probably without parallel, of an extensive body of water on the Atlantic slope stocked by nature with fish from the Pacific. The trout of the Yellowstone Lake are to some extent infected with a disease which renders them unfit for eating. In earlier times particularly, this condition was generally prevalent. But more recently the disease seems to be disappearing, and in time it will probably die out altogether. In 1889 and 1890, the United States Fish Commission undertook to stock all the fishless streams in the Park, and planted about 83,000 yearling trout in the various streams and lakes. The varieties were Brook, Lake, Loch Leven, and Von Behr trout. Recent examination of these plants shows that all have taken decisive root, and that within a few years there will not be a hidden stream or lake in the Park which will be without its attractions for the sportsman. CHAPTER VII. FLORA OF THE YELLOWSTONE. The most conspicuous feature of the Park flora is the wide extent of forest growth which covers some eighty-four per cent of its area. This is the more noticeable because the surrounding country below the mountains is practically treeless. The Park forests consist almost exclusively of pine and fir. The trees are generally tall and slender and of little use for lumber. They are usually unattractive in appearance, although in some places among the mountains the spruce and fir attain a size, form and hue of foliage that are exceedingly beautiful. Among the several species may be noted the following: Black pine (_Pinus Murrayana_) so called from the dark hue of its foliage when seen in dense bodies. Red fir (_Pseudotsuga Douglasii_) the largest variety in the Park, sometimes attaining a diameter of five feet. Balsam (_Abies subalpina_). It flourishes near the snow fields and is the beauty of the forest. Spruce (_Pinus Engelmanni_). Like the preceding it flourishes at high altitudes. It is tall and slender, and is good for lumber. Red cedar (_Juniperus virginiana_) is found to a limited extent. Poplar or aspen (_Populus tremuloides_) flourishes among the sheltered foot-hills. Dwarf maple is occasionally found. Willow thickets abound in great abundance.