The Flora of the Cayuga Lake Basin 445 



219, soils of undefined texture, mostly medium, 163, heavy soils 7. This striking pre- 

 ponderance of light-soil plants over heavy-soil plants was unexpected. However, 

 it accords fairly well with experience, in that better botanizing, as far as the number 

 of rare plants is concerned, is found on gravel and sand than on clay, especially in dry 

 soils. The preference of plants of the different geographical affinities for particular 

 soils is interesting and was not wholly expected. 



Though the relation between soils and native plants is a subject yet too poorly 

 understood to allow much detailed information in this work, a very serious attempt 

 has been made to include under each species in the text as much knowledge as could 

 be obtained regarding its specific requirements. Also, under the range of each species 

 the fact of its occurrence or its absence on the Atlantic Coastal Plain has been noted. 

 Since the plants of that region so generally inhabit light sandy acid soils, the occurrence 

 or the nonoccurrence of a species there often throws light on its soil requirements. 

 Investigation of the soil relations of the native plants is urgently needed and can 

 scarcely fail to furnish important information for the plant geographer. Even more 

 important will be the information furnished the agronomist, for it has been shown 

 that in many cases the wild plants are more sensitive to small differences in composi- 

 tion of the soil than are chemical and physical analyses, and hence the data so obtained 

 should be useful in supplementing those obtained in the usual way. 



CLIMATE 



The effect of climate on the distribution of plants in the Cayuga Lake Basin has 

 not been thoroughly studied. Probably the climate is a more potent factor here 

 than it usually is elsewhere in an area of equal size, except in mountainous regions, 

 as there is a not inconsiderable diversity of altitude and a marked local effect of the 

 lake water. In general, the basin lies in the Transition Life Zone, but a distinct 

 Austral element is found in the lake valley, and a small Canadian element on the 

 hills, in the McLean region, and on the northward-facing slopes of the ravines. 



The Cayuga Lake Basin lies in the general forest belt of the eastern United States, 

 and has an average yearly rainfall of about 85 centimeters (33.4 inches). The 

 yearly average temperature for Ithaca is about 47° F., and for the McLean region 

 approximately 45° F. The average monthly temperatures for Ithaca, in degrees 

 Fahrenheit, are : 



January 



24.5° 



May 



57.1° 



September 



61.8' 



February 



24.1° 



June 



66.0° 



October 



51.0' 



March 



32.4° 



July 



70.6° 



November 



39.0' 



April 



44.9° 



August 



68.2° 



December 



28.7 C 



The average date of the last killing frost in the spring, at Ithaca, is May 10, and that 

 of the first killing frost in the fall is October 10. The lowest temperature reached 

 during a period of forty-six years is -22° F., and the highest is 102° F. 



As factors of the general topography which affect plant distribution, the lake and 

 the hills are important. The influence of the great depth of the lake en the tem- 

 perature of the water has been mentioned. The lake is colder in early summer, and 

 warmer in late autumn, than a shallow body of water. That some modification of 

 the air temperature should be caused by this condition is to be expected, and such 

 is the case. The temperature of the lake unquestionably influences the develop- 

 ment of the vegetation in its immediate vicinity. As Dudley has stated, plants on 

 its shores usually develop a week or more later in spring than they do in the 

 neighboring ravines and warm valleys around Ithaca. During the first half of 

 November the blue flowers of Aster laevis and the white panicles of Aster sagitti- 

 folhis still remain in considerable abundance along the lake shore, long after those 

 near Ithaca have matured and faded. The effect of the lake can at times be 

 detected by the presence of a cloud bank on the side of the valley away from the 



