. Carnegie Institution of Washington publication. CORRELATION OF DISTRIBUTIONAL FEATURES. 533 trees, not on the ideal basis of the ecological distribution of all species of that type, but on the only basis which is now practicableâthe geographical distribution of the most abundant species. It will be noted that there are a number of cases, particularly among the temperature conditions, in which the upper climatic extreme grows higher as we pass from the center (with 13 species) through the subcenter (with 8 or more species) into the fringe (with 1 to 7 species). Thus, the number of species of
. Carnegie Institution of Washington publication. CORRELATION OF DISTRIBUTIONAL FEATURES. 533 trees, not on the ideal basis of the ecological distribution of all species of that type, but on the only basis which is now practicableâthe geographical distribution of the most abundant species. It will be noted that there are a number of cases, particularly among the temperature conditions, in which the upper climatic extreme grows higher as we pass from the center (with 13 species) through the subcenter (with 8 or more species) into the fringe (with 1 to 7 species). Thus, the number of species of deciduous trees grows less as the frost- less season grows longer, as the number of hot days increases, as the number of cold days increases, etc. In several cases the extremes are nearly the same for the center and the subcenter, or for the subcenter and the fringe. In the case of humidity we have no deciduous trees growing in the lower half of the gamut of this condition; with increasing humidities above per cent we have an increasing number of deciduous species; on approaching the region with highest humidities we first leave the fringe, then the subcenter, and finally the center. Rather wide amplitudes characterize all oif the temperature condi- tions, and in most cases the conditions of the subcenter and fringe shade off very gradually from the conditions of the center. The minimum number of cold days is the same for all three areas, inasmuch as all of them range into the region with no cold days. A much more irregular set of relations is exhibited between the extremes for the moisture conditions of the three areas. The shortening of the longest rainy period brings us rapidly from the center to the limit of the entire group. Increasing evaporation also brings us, within very narrow limits, from the center to the edge. TCMPCRATUnC lAYS IN Normal Frostlcsb Season (F. S.) loT Days, F. S. OLD Days, F. S. 'HYSIOLOGICAL SUMMATION, F. S. lORMAL DailV Mean, coldest 14 days o
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