254 



If we sum up the second, third, and fourth series of fio:ures we 

 finally obtain the sum total of the effective radiation received during 

 the whole interval from germination to ripening, as given in the 

 following table : 



Total radiation received from 

 germination to ripening. 



Rela- 

 crop. 



1873. 

 1874. 

 1875. 

 1876. 

 1877. 

 1878. 

 ^879 . 



5,223 

 5,342 

 5,537 



5,919 

 5,344 



6,173 

 5,454 

 5,856 



5,614 



5,924 

 5,438 

 5,676 



5,011 

 5,910 



4,240 

 5,512 



4,658 

 5,237 

 5,561 



4,913 

 5,433 

 5,569 

 6,345 



4,436 

 5,263 

 5,266 

 6,145 



19.0 

 26.5 

 22.5 

 15.2 

 11.1 



Average of 6 years. 



5,102 5,288 5,550 5,645 



The relative value of the wheat crops, as observed at two stations, 

 is given in the last column of the preceding table, and the comparison 

 of the figures shoAvs that a deficiency of sunshine has a decided effect 

 in diminishing the relative value of the crop ; but the converse is not 

 true, for we may have an excess of sunshine and still get poor crops, 

 owing to a deficiency of rain or irrigating water. In fact, the pre- 

 ceding study only shows the nature of the influence of the solar 

 radiation ; the exact quantitative effect on the amount of the crop must 

 vary with the irrigation or rainfall, with the fertilizers applied to 

 the soil, and with the peculiarities of the seed. 



As to the rainfall, it was in the preceding cases distributed as shown 

 in the following table: 



- From these figures we conclude that the excess of rain in the wheat 

 season of 1878-79, which would have been advantageous with a clear 

 sky, as in Egypt," was at Paris accompanied by too little sunshine, 

 and therefore the crop suffered. For a given quantity of sunshine a 

 certain quantity of water is best for the crop; if the sunshine is 

 diminished the plant can not use so much water, and that must be 

 correspondingly diminished. 



a Or as in the case of irrigation in tlie arid portions of tlie United States. — C. A. 



