Temperature and Rainfall. 63 



moisture, the preponderating influence which the character of 

 the seasons exercises over the growth of our crops is no more 

 than might be expected. Though the connection between 

 meteorological phenomena and the progress of vegetation is 

 not yet so clearly comprehended as to enable us to estimate 

 with any accuracy the yield of a crop by studying the 

 statistics of the weather during the period of its growth, the 

 present attempt is, nevertheless, a valuable contribution 

 towards such an object. 



Temperature and rainfall are the chief factors demanding 

 attention, but it is necessary to distinguish between the 

 total heat and the total rainfall of a season, and the distribu- 

 tion of temperature and of rainfall over the different periods 

 of the season. It is obvious that a given amount of rain 

 equally distributed through the spring and summer in each 

 of two seasons, will have a very widely different effect on 

 vegetation in the two cases, if the one season should be a hot 

 and the other a cold one. On the other hand, if the temper- 

 ature of the two seasons be the same, but the rainfall very 

 different, so also will the effect on vegetation be very different. 

 The defect of our climate for the production of wheat is 

 apparently more connected with an excess of moisture than 

 with a deficiency of heat, during the periods of active growth 

 and maturing. It is, in fact, when a cold season, or one of 

 only moderate temperature, is accompanied by an excess of 

 rain, that the yield of our wheat crops is the most defective. 



During the present century, each of the following years 

 was more or less remarkable so far as the growth of the 

 wheat crop is concerned; 1816, 1832, 1833, 1834, 1835, 1853, 

 1854, 1857, 1860, 1863, 1864, 1868, 1870, and 1879. Of 

 these, 1816 and 1879 have the reputation of yielding the 

 two worst wheat crops within the period included by those 

 dates ; on the other hand, 1834 is generally referred to as 

 one of the most productive years of the century. Four 

 seasons of reputed very high productiveness which occurred 

 before the commencement of the Rothamsted experiments, 



