239 



trees and oxtimining them very freciuently Hoffinann seeks to deter- 

 mine how accuratel}' the date of the beginning of vegetation or the 

 flow of sap can be determined by the swelling of the buds and the 

 visible cracking of the delicate pencil lines of paint. lie finds that 

 the date can be determined to within one day when spring comes on 

 rapidly, but within eight days when it comes very slowly. The cor- 

 responding uncertainty or variability of the sums of the maximum 

 sunshine thermometer from the swelling of the buds up to the date 

 of the first blossom, for instance, for Castanea vulgaris, is -t per cent 

 while the uncertainty of similar sums, counting from January 1, 

 is only 1 per cent. These and similar data are only deducible from 

 observations made upon the same tree or bush from year to year; 

 the variations are materially increased when different plants in dif- 

 ferent localities are observed ; moreover, they are based upon observa- 

 tions for only four years, which period is not long enough to give a 

 reliable value of the relative inicertainties. As in previous cases in 

 making up these abstracts, I give Hoffmann's actual figures in the 

 following summary, which I have compiled by collating the few 

 observations published by him in the Zeitschrift during the j^ears 

 1870-1890. I have selected only the few plants for which he has 

 published the sums for several years or for two localities, so that 

 comparisons may be made and a judgment arrived at as to the pro- 

 priety of his method. It will be observed that Hoffmann has, when 

 possible, observed the same tree or bush from year to year, so that 

 the problem of the influence of heat is much more definite than when 

 different plants or a general mass of plants is observed; but, on the 

 other hand, single plants are more liable to irregularities produced 

 by special disturbances which would exert no appreciable influence 

 on the average of a large number of similar plants. 



Temperature sums at Glessen (Iloffmanirs method) from the first sivelliii(/ of 



the buds to the first blossom. 



[Z. O. G. M., Vol. XVII, 1882, p. 127. All in Reaumur degrees.] 



Castanea vulgaris . . . 

 Catalpa syringafolia. 

 Lonicera alpigena: 



First specimen . . . 



Second f pecimen 

 Persica vulgaris: 



Fir.st specimen 



Second specimen. 

 Syringa vulgaris: 



First specimen . . . 



Second specimen. 

 Vitis vinifera: 



First specimen . . . 



Second specimen. 



2,142 



2,085 

 1,984 



1,058 

 1,058 



1,315 

 1,181 



1,04(J 



me, 



2,317 

 2,547 



1,014 

 1,032 



1,248 

 1,16<> 



1,5:^1 

 1,222 



