CONTINENTAL VS. MARINE CLIMATES IN EUROPE 



495 



has been given to the investigation of the relation between climate and 

 the rate of growth of trees. It has there been shown that if the proper 

 methods are employed, even a small number of trees will give a fairly 

 accurate record of the particular climatic elements on which growth 

 chiefly depends. The method was first dcA^eloped by Prof. A. E. Douglass, 

 who measured the yellow pine in Arizona. His methods are described by 

 himself in "The Climatic Factor." In Germany, at Eberswalde, near 

 Berlin, he has made some measurements which are of importance in the 

 present connection. The results are shown in figure 2. The lower curve 

 is that of sun-spots. The curve above it shows the growth of thirteen 

 pine trees. This has been smoothed to eliminate minor vagaries, but not 

 in such a way as to influence the main sinuosities. It has also been cor- 

 rected in order to eliminate the effect of the more rapid growth of trees 



20 30 



40 



1850 



60 70 



80^^ 9 



3 1900 19 



IC 













J 





<» 



M 





100 



v./^ 



V ..^ 



L / 



X y ■ 



v/ 



\ 



^ 



A 





100 



A 



A 



V 



/ 



\ 



v 



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^ \ 



f. 



0. 



\f" 



V^ 



x/ 



sV 



V. 



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Figure 2. 



-Growth of Trees at Eherswalde, Germany (middle curve), and Sun- 

 (loioer curve). (After Douglass) 



Note. — -The smaU upper curve indicates the number of summer storms (April-November) 



in youth than in maturity and old age. These processes have been dis- 

 cussed in full in "The Climatic Factor," and the reader who would under- 

 stand them is referred to that publication. It will there be seen that 

 the whole matter is mathematical, and that the personal opinion of the 

 investigator can not materially influence the results. The extent to which 

 the two main curves of figure 2 agree is remarkable. With one exception 

 the seven maxima of the sun-spot curve are faithfully reproduced in the 

 tree curve. The minima agree equally well. The only exception begins 

 in 1892 and continues until 1899. It has not been possible to ascertain 

 its cause. It may be due to some meteorological condition or to some 

 such thing as insect pests. If the growth of the trees had not been 

 checked, its curve would probably have agreed closely with that of the 

 sun-spats. This conclusion is sti-engthened by the fact that in 1900 we 

 have a little minimum corresponding to the minimum in the sun-spot 

 curve, but occurring slightly before it, as is usually the case. 



In order to determine exactly what climatic conditions are indicated 

 by the tree curve of figure 2, I have worked out two sets of correlation 



