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that the temperatures useful to the phmt vary with the species and 

 are decidedly above freezing, therefore students have taken other 

 limits. Thus Gasparin and ITerve Mangon adopt 0° C. for the 

 initial temperature in the growth of wheat. In order to ascertain 

 the proper method of counting temperatures Angot has accomplished 

 the labor of prosecuting three parallel computations by tliree difi'erent 

 methods, as follows: 



(A) First method. — By observations of daily maximum and mini- 

 mum temperatures. In this method Angot has examined separately the 

 observed maxima and minima of the thermometer in the shade. After 

 rejecting all observations below 6° C., he subtracts 6° C. from all the 

 others and takes, the separate sums of the remaining maxima and 

 minima for each month and then the average of these two sums, 

 which consequently represents a sum total of heat received during 

 the month in excess of ()° C. 



(B) Second method. — By the daily means. In this method the 

 mean of each day is first computed by taking the average of the 

 maxinunn and minimum; 6° C. is then subtracted from each of 

 these daily means and all negative remainders are rejected. The 

 sum of the positive remainders represents the sum total of heat 

 received in excess of 6° C. 



(C) Third method. — By maximum temperatures alone. In this 

 method, which is a modification of that proposed by Hoffmann, a max- 

 imum thermometer is exposed to the direct rays of the sun and the 

 sum total of the maximum temperatures is used by Hoffmann. But 

 Angot prefers to use the maximum thermometer in the shade, as in 

 the first method, and, as before, takes the sum total of all the posi- 

 tive remainders after subtracting 0° C. 



In all these methods the principal difficulty is to fix the epoch 

 from which the summation should begin. Sometimes the date of 

 sowing has been adopted as this epoch, but from the date of sowing 

 up to the date of sprouting the seed and the young plant are sub- 

 jected only to the temperature of the soil, and not to that of the air, 

 which often differ considerably. It would perhaps be better to 

 start with the date at which the plant appears above the earth, but 

 the date of sprouting is not generally given by observers. He there- 

 fore provisionally adopts the 1st of December as the point of depar- 

 ture and calculates the sum total of temperatures for the nine stations 

 in France for which the dates of flowering and harvesting of winter 

 wheat have been best determined for the years 1880 and 1881. The 

 agreement among themselves of the numbers calculated by these 

 three methods for nine stations and two different years is such that 

 no decision can be arrived at as to which method is the best, and 

 such decision is reserved for a future study of other harvests. 



