213 



plants that wore observed at Brussels 

 miles south of 8t. Petersbure: : 



and at Poulkova. which 



In takino^ these sums, which all relate to positive temperatures on 

 the centigrade thermometer only, Linsser begins with April 8 at 

 Poulkova, because on that date the gradually rising daily tempera- 

 tures pass through the freezing point. -It would have made no 

 difference if he had begun with January 1, or December 1, or with 

 the date of lowest mean temperature, which would be about the 

 middle of January. On the other hand, for Brussels his sums begin 

 with January 15, which is the date at which the lowest mean daily 

 temperature occurs, which temperature is about -|-2-'">° C. so that 

 if he had begun with January 1 there would have been a constant 

 slight addition to all the numbers in that column. The dates of 

 blossoming are given in days counting consecutively from the 1st of 

 January, and may be converted into the days of the month or vice 

 versa by the following table : 



Day of the 

 year. 



January 

 February 1 

 March 1 

 April 1 - 

 Slay 1 _ . 

 Juuf 1 . . 

 July 1.. 



If we take the dilference between the sums of the temperatui-es for 

 the first and seventh grou])s of plants in the preceding table we obtain 

 for Brussels 1,972° C, and for Poulkova 1,280° C, or a difference of 

 about 700° C., which corresi)()nds to about forty days at Poulkova. so 

 that we must immediately conclude that the same stages of develop- 



