with De Candolle in his plea for a climatic laboratory. It is evident 

 that in such an institution one may reproduce to perfection the cli- 

 matic conditions under which a given seed was grown, and thus 

 insure a maximum crop; or. on the other hand, by successive culti- 

 vations, under successive slight changes in the artificial climate, may 

 so modify the seed as to produce a new variety with a fixed habit of 

 growth adapted to any natural climate that the farmer has to deal 

 with. The laws of acclimatization that naturally follow from Lins- 

 ser's investigations, and, in fact, from general experience in all parts 

 of the world, point to this as a most important field of future useful- 

 ness. It is thus that we may hope to accelerate the natural course, 

 which, on the one hand, has already produced grains adapted to the 

 Russian steppes, and, on the other, will eventually evolve those 

 adapted to the vicissitudes of our own arid regions and i30ssibly our 

 severe Alaskan climate. 



3. The statistical method of ascertaining the effect of a climate on 

 the resulting crop consists in comparing the statistics of the succes- 

 sive annual harvests in the country at large with the statistics of the 

 prevailing climatic conditions. At the close of this report I have 

 given a large collection of data of this kind, sufficient, I think^ to 

 ihow that this method is very unsatisfactory because of our ignorance 

 3f the many details that must be considered in discussing the statis- 

 tical figures. I have compiled these elaborate tables for the United 

 States from the data given by the former Statistician of the Depart- 

 ment of Agriculture, Mr. J. R. Dodge, and his able assistant, Mr. 

 Snow, and have indicated a method of treating these figures which 

 will, I think, eventually give us the best results that they are capable 

 of affording, and will be, perhaps, sufficiently accurate for the needs 

 of the farmer, the merchant, and the statesman, but Avhich can scarcely 

 respond to the exact demands of agricultural physics. The great col- 

 lection of data given in the reports of the Tenth and Eleventh cen- 

 suses of the United States for the crop years 1879 and 1889 will, 

 I hope, tempt some one to an extended study for those years. 



I shall not devote much space to the question of the relative influ- 

 ence of forests and cultivated fields on the temperature and moisture 

 of the local air. This has become a special studv on the part of those 

 devoted to forestry, and the papers of Professor Ebermayer (1873), 

 Muttrich (1880), Nordlinger (1885), and others" teem with figures to 

 show that in the heart of an extensive forest the mean daily varia- 

 tions of temperature or the range from minimum to maximum is, on 

 the average, from 2° to 5° C. less than in the open air just outside the 

 forest, while a similar difference of only 1° to 2° C. exists for the 



.he full titles of the works referred to in this report will be found in section 

 Bibliography," Part IV. 



