Life zones, as defined in relation to plant and animal life, are areas inhabited by more or less definite groups of plants and animals. The classification of these zones which is accepted by many biologists was devised by Dr. C. Hart Merriam, who named six zones; the Arctic-alpine, Hudsonian, Canadian, Transition, Upper Sonoran and Lower Sonoran. If one travels from the Southwestern United States into the high country of the Rockies or the Pacific Northwest, he will pass through all six of these zones, beginning with the Lower Sonoran, or low desert zone, through the Upper Sonoran, or high desert, and so on through the others until the highest, or Arctic-alpine Zone is reached. The area immediately adjacent to Puget Sound, for example, falls within the Transition Zone. Moving inland toward Mount Rainier, one passes from the Transition into the Canadian Zone, usually a short distance inside the park boundaries, and the major portion of Mount Rainier National Park is within the upper three zones. Temperature is the basis for the separation of these zones, and temperature, as we know, is affected by both altitude and latitude. In general a difference of 1,000 feet in altitude is equivalent to a difference of 300 miles in latitude. Variation in latitude explains the high elevation of tree line in the southern Sierra Nevada of California in relation to the comparatively low limit of tree growth in northern British Columbia or Alaska. Variation in temperature explains the tremendous difference in size and variety of tree species at 2,000 feet and at forest line, 6,500 feet, on Mount Rainier. On a very high mountain we might find all six of the life zones represented. The mountain presenting such a condition, however, would necessarily be located in a more southern latitude than Mount Rainier. Four life zones are represented in Mount Rainier National Park: the Transition Zone, which occupies the lower elevations of the park up to 3,000 feet; the Canadian Zone, which, with the exception of the Transition area, extends from park boundaries to about 5,000 feet; the Hudsonian Zone, with an altitudinal range of from approximately 5,000 to 6,500 feet; and the Arctic-alpine Zone, from 6,500 feet to the summit of the Mountain.