. Carnegie Institution of Washington publication. 550 COERELATION OF DISTRIBUTIONAL FEATURES. suggestion of their importance as limiting the plant. Its distributional edge, extending from central Michigan to the mouth of the Colorado River, is 2,300 miles in length, which in itself suggests that very dis- similar constellations of conditions are involved in its limitation in sections of this line. In a plant of palustrine habitat it is not surprising to find that the normal moisture conditions of upland habitats have no apparent importance. We find Cephalanthus occur- ring in locali
. Carnegie Institution of Washington publication. 550 COERELATION OF DISTRIBUTIONAL FEATURES. suggestion of their importance as limiting the plant. Its distributional edge, extending from central Michigan to the mouth of the Colorado River, is 2,300 miles in length, which in itself suggests that very dis- similar constellations of conditions are involved in its limitation in sections of this line. In a plant of palustrine habitat it is not surprising to find that the normal moisture conditions of upland habitats have no apparent importance. We find Cephalanthus occur- ring in localities where the moisture ratios approach their minimum values for the United States, and extending from there halfway through the gamut of values for this compound condition. It also encounters extremely low values for the normal daily precipitation and high values for the number of days in the longest dry periods. These con- ditions, however, have no apparent influence on the plant in the habitats where it occurs, although they are probably responsible for the fact that there are very few favorable habitats for it in the localities where these extremes are registered. In the San Joaquin Valley the atmospheric conditions are extremely arid, but there are numerous areas of moist soil, and Cephalanthus is there abundant. It is by no means true that all palustrine or swamp plants are able to withstand extremely arid atmospheric conditions if they are supplied with an abundance of soil-moisture, and only a relatively small number of the plants associated with Cephalanthus in the southeastern United States are found growing with it in southern Arizona and the San Joaquin Valley. It is in the eastern half of its range that Cephalanthus encounters the greatest amplitude of temperature conditions. It is there found in localities with no hot days, as many as 137 cold days, where the TlnmiMTVKC Oat* ih Normal Frostlcs* Season iF. S.) Hot Oat*. F. S. Colo Days, F. S. Phvbiolocical Summatio
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