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 apphes 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 earler 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 
eradual progress northward of the development of vegetation as 
spring advances. 
