181 



with regard to wheat in America after an extensive research, bnt 

 within the past few years mucli more iittention has been given to this 

 subject. 



The differences between the quantities of heat required in England 

 and America and the differences in the varieties of the wheat were 

 apparent to Lippincott. Thus, he finds that in England the lengths of 

 the periods and the sums of the temperatures were as foUows: In 

 1860 a period of 59 days and a sum of 3,562° F. ; in 1861 a period of 

 50 days and a sum of 3,225° F, ; in 1862 a period of 56 days and a 

 sum of 3,406° F. The reduction of the mean temperature during 

 two months of 1853 by merely 2° F. cut off one-third of the crop and 

 brought a famine that was already foreseen in July, 1853. On the 

 other hand, it increased the exportation of wheat and flour from the 

 United States from $14,000,000 in 1852 and $19,000,000 in 1853 to 

 $49,000,000 in 1854. 



A careful study of the sum totals of rainfall, temperature, and sun- 

 shine should enable one, in general, to foresee similar failures and 

 corresponding successes in the crops of any region. 



QUETELET. 



The suggestive, but sketchy, studies of earlier writers on thermal 

 constants Avere supplemented by more elaborate investigations and 

 calcuhitions of statistics by Quetelet (1849) in his Climate of Bel- 

 gium, from his own summary (p. 62), etc., I take the following 

 notes : 



The details hitherto given show sufficiently that the relative condi- 

 tions of vegetation change at all times of the ,vear in two countries 

 situated at a distance from each other. Acceleration and retardation 

 are quantities essentially variable, and it is erroneous to say that one 

 locality has its budding period ten or twenty days sooner, for 

 example, than another. This difference may be correct for one sea- 

 son of the year and entirely wrong for another; and, moreover, we 

 can onlv pretend to state a fact which applies to the majority of 

 plants. ■ 



Nevertheless the differences in the periods of budding are not so 

 variable but that we can assign to them values very useful to consult 

 in jn-actice. On the other hand, science needs to establisli some well- 

 determined facts in order to arrive later at the knowledge of the 

 laws upon which these variations depend. I believe that in the 

 a(;tual state of things I shall be able to settle upon the following 

 epochs, in order not to multiply too much the terms of comparison. 

 Moreover, the "numerical tables justify, to a certain extent, the dis- 

 tinctions which I lay down. 



Let us first observe that the awakening of the })lants is brought about 

 by the cessation of the cold, and it suflices to consult the tables of 

 temperatures for the different countries to determine the average 

 epoch at which many plants will put out their leaves or their flowers. 

 These first indications, which it is well to collect, still do not deter- 

 mine, however, the general niovenient of vegetation which may 



