242 



sums that agree so well with those found at Giessen that Hoffmann 

 thinks no better can be expected. 



In the Zeitschrift for 1885 Hoffmann continues to give the com- 

 parative observations at Giessen and Upsala, and remarks that the 

 question is not as to whether his method is correct and the others are 

 wrong, but as to which of all methods is even a little better than the 

 others. Of these others only one can, he thinks, be compared with 

 his own, viz, that of Karl Fritsch, who takes the sum of all positive 

 mean daily shade temperatures. Hoffmann applies Fritsch's method 

 to the observations at Giessen and Upsala and finds the argument not 

 in its favor. He also tries another form of thermometer, viz, the 

 so-called black bulb in vacuo, but finds it too sensitive, which he 

 thinks is because its bulb is too small. 



In the Zeitschrift for 1886 (p. 546) Hoffmann gives a summary of 

 observations at Giessen and Upsala during 1886. In general the 

 sums are smaller at Upsala and so also for high Alpine stations. He 

 is thus led to the laws established by Karl Linsser, as published in 

 St. Petersburg in 1867 and 1869, which laws he expresses as follows : 

 "• Every wild plant has in the course of time so adapted itself to the 

 surrounding local climate that it utilizes this climate to the best 

 advantage. For any given phase of vegetation it uses a certain pro- 

 portional part of the available annual sum total of heat. Thus, if 

 the annual sum at Venice is 4,000 and if the corresponding sum at St. 

 Petersburg is 2,000 and if the plant utilizes one-fourth in order to 

 bring it to the flowering stage, then it will require 1,000 at Venice 

 and 500 at St. Petersburg." From Linsser's law he concludes; (1) 

 plants that have been raised in the north and are transplanted 

 to the south reach their phenological epochs earlier than plants 

 already living there, while southerly plants carried to the north are 

 retarded as compared with those already acclimatized; (2) plants 

 raised on colder highlands when transplanted to the warmer low- 

 lands have their epochs accelerated as compared with those already 

 domesticated; plants raised in the lowlands and transplanted to the 

 colder highlands develop more slowly than the acclimatized plants. 



In the Zeitschrift for 1886 (p. 113) Hoffmann determines the rela- 

 tive retardation of vegetation as determined by the dates of the first 

 blossom of several plants at different altitudes. The result is for 

 the Pyrus communis (pear tree) and allied varieties a retardation of 

 3.7 days per 100 meters, and corresponding to this a retardation 

 of 2.8 days per 1° of latitude. The analogous data for Pyrus malus 

 (apples) are 2 days per 100 meters and 4.4 days per 1° of latitude. 

 Charts are given showing by means of isophenological lines the 

 gradual progress northward of the development of vegetation as 

 spring advances. 



