534 CORRELATION OF DISTRIBUTIONAL FEATURES. 



The narrowest amplitudes for the center are in the three moisture 

 ratios and in the number of days in the longest dry period; and in all 

 four of these cases a slightly wider amplitude of conditions brings us 

 to the extremes for the fringe. A comparison of plate 5 with plate 59 

 shows that the whole region occupied by the center, subcenter, and 

 fringe is very nearly confined between the isoclimatic lines for mois- 

 ture-ratio values of 0.60 and 1.10, although the fringe enters regions 

 with higher values. The range from 0.80 to 1.10 is scarcely exceeded 

 by the center. The isoclimatic line for dry periods of 50 days is close 

 to marking the western limit of the fringe of deciduous trees. In the 

 center the extreme range is from 4 to 56 days, values above 50 being 

 extremely local in this region, however. 



Figure 43 should be compared with figure 31, which shows the 

 climatic extremes for the Deciduous Forest region. The extremes for 

 the Deciduous Forest lie, in general, outside those of the center of the 

 13 common species and inside those of the fringe. 



Liriodendron tulipifera (fig. 44).— The area in which this tree is 

 of commercial importance may well be regarded as its ecological 

 center, while the region in which it occurs too infrequently to have 

 such importance may be designated as its fringe (plate 9). The center 

 for Liriodendron lies almost wholly within the center for the 13 decid- 

 uous trees just treated, and its distributional limit is similar to that of 

 the subcenter of the deciduous trees, although not extending quite so 

 far west. The conditions for the center and fringe of Liriodendron 

 have been shown by pairs of graphs in figure 44. 



The region of greatest abundance for Liriodendron is one of the very 

 few botanical areas investigated in which the edge lies entirely within 

 the United States and is nowhere formed by a coast-line. The fact 



O/iT* IN NexM*!. FiioaTitsa Smmn (F. S.> 



Hot D*v*, F. S. 



Colo D»«. F. S. 



PHVtioi.ooic*L Summation, F. S. 



NoKMAi. Oailt MC«N, COIOCST 14 D»S Of YUN 



Normal Daily Mcan. Year 



PRtCimTATION 



Normal Daily Mcan, F. S. 

 Oats in lonoist Normal Rainy Pcriod. F. S. 

 Day* in lonocrt Normal Dry Pcriod, F. S. 

 Mcan Total. Ycar 



cvaporation 

 Daily Mcan, laef-B, F. S. 



Moisture Ratios 

 Normal p/E, F. S. 

 Normal ir/E, F. S. 

 Normal P/E, Ycar 



humioitt 

 Normal Mcan, F. S. 



Sunshine ^ 



Normal Daily Duration, F. S. I :^z^^amiSi^^^^^^^^^m^^^^^m 



MOISTURC-TCMPCRATURf iNBICn 



NORVAL P/t ■ T. F. 8., Pmybiolooicai Mctmob E 



Fig. 44. Climatic extremes for Liriodendron; upper blocks for center, lower for fringe. 



