INTRODUCTION 35 



of the "setting" of the buds is originated. The writer regrets 

 that he has not had the necessary time to apply, for at least a 

 part of our flora, the very interesting results of Raunkiaer's 

 "Growth Forms" to the present book. The recent appearance of 

 this work and the great labor necessary for its application to our 

 area, precluded what, it is hoped, may be the most effective study 

 of the relationship between a flora and the climatic factors that 

 has yet appeared.* It may form the basis of a future study. 



59. During 1905 Dr. Cleveland Abbe brought out his work on 

 the effect of climate on crops,! in which he treated the temperature 

 factor from a somewhat different viewpoint. He satisfied himself 

 that maximum and minimum temperatures, and that any method 

 of reckoning accumulative temperatures were not the vital factors 

 in this problem. His method, in short, was to take account not 

 of the severity of the frosts but of the length of the growing season. 



60. Experimental proof of the very close relation between the 

 length of the growing season and crops is not lacking. The 

 government, by moving northward certain strains of wheat to 

 regions with a progressively diminishing growing season, has been 

 able to get crops in regions, that, if the move had been made in one 

 season, would have been impossible. The method of determining 

 this length of the growing season is to add the number of days 

 between the last killing frost in the spring and the first killing 

 frost of autumn. 



61. The application of this idea to our local flora range has 

 brought out some interesting points. Examination of the map 

 {pi. 5) shows that the length of the growing season in the Catskills 

 and mountains of Pennsylvania is 117-123 days, at Cape May it 

 is 220 days. Here is a difference of over three months in the grow- 

 ing season. All the figures have been determined by averaging 

 the number of days between the killing frosts, for every station in 

 the range, where records have been kept for ten years or more. 



62. On the map {pi. 5) will be found a dark line running in a 

 northeast-southwest direction. Every weather station north of 



* Raunkiaer, C. Bot.Tidssk. 26: 1904; 30: 1909; 33: 1912. And other papers. See 

 also Jour. Ecol. 1: 16-26. 1913. and Paulsen, O. Studies on the vegetation of the 

 Transcaspian lowlands. Second Danish Pamir Expedition Reports. Copenhagen. 

 1912. 



t Abbe, C. First report on the relation between climate and crops. Bull. U. S. 

 Weather Bureau 36: 1-386. 1905. 



