Within its natural range in Wisconsin, white cedar (Thuja occidentalis L.) displays the ability to persist in a wide range of habitats. Figure 1 indicates the range of white cedar in Wisconsin. It forms dense swamps on low, poorly drained topography and is commonly found on upland, well drained sites as well. This ability of white cedar has long been recognized and has been attributed to a wide degree of adaptability possessed by the species. Potzger (1941) has suggested that white cedar in northern Michigan possesses ecotypes because of its presence on upland and lowland sites in that area. There has not been, as yet, any critical investigation made of this phenomenon to substantiate the idea that ecotypes exist in white cedar. Taxonomically, there are no subspecies or varieties recognized in this species, there being no distinguishable morphological differences between white cedar found on any site. This study was undertaken to determine whether ecotypic variants exist in the white cedar population in Wisconsin. In northern and eastern Wisconsin, the extremes in white cedar habitats can often be found geographically close together, sometimes within a few hundred feet. Wide geographical distances are involved in many demonstrations of ecotypes in other species. Pauley and Perry (1954) have shown that ecotypes occur in the wide ranging species of Populus deltoides Marsh. and P. trichocarpa Torr. & Gray in response to photoperiodicity. Vaartaja (1954) has determined the presence of photoperiodic ecotypes within Pinus sylvestris L. and Alnus incana (L.) Moench. as a result of studies on material collected from northern and southern latitudes in Finland. Wright (1944a, 1944b) found three ecotypes in both white ash (Fraxinus americana: L.) and red ash (F. pennsylvanica Marsh.). These ash ecotypes are rather widely separated geographically and are differentiated on their ability to withstand cold. Within a much smaller geographical area, central California, McMillan (1956) has indicated that important edaphic ecotypic variation exists in species of Cupressus and Pinus whose ranges include serpentine and nonserpentine soils. Ecotypes occurring rather close together on different soils are probably of greater ecological importance than those existing hundreds of miles apart on the same soil. The recognition of local ecotypes is of particular importance in phytosociological studies. The procedure used in this study involved the collection, for transplantation purposes, of naturally occurring white cedar seedlings from both upland and lowland habitats throughout the white cedar range in Wisconsin, and also the collection of seed from the same sites for germination tests and growth experiments. A presentation of the methods and results will be given first for the seedling transplants, followed by a similar outline for the seed germination and growth experiments. This work was supported in part by the Wisconsin Conservation Department, with Federal Aid to Wildlife Restoration funds under PittmanRobertson Project Number W-79-R. The author wishes to extend his appreciation to Dr. J. T. Curtis for critical reading of the manuscript.