ESTIMATION OF THE HEAT NECESSARY TO tJKOWTU. 



565 



of development, iu uiauy cases, much more clearly exhibits the clinuite of a district 

 than the readings of instruments erected in the places in question. The so-called 

 phfenological observations, that is, the determination of the awakening of nature at 

 the close of the winter, or at the end of the summer drought, the ascertaining of the 

 times at which growth and blossoming roach their umximuin, and the fixing of the 

 period at which the organism, on account of the unfavourable external conditions, 

 falls into a winter or summer sleep, are consequently of interest even if we are 

 unable to reckon the heat constants for the commencement of these phenomena. 

 The i-esults of such phrenological observations have been already made use of 

 repeatedly on pp. 519 and 525, and it has been there shown how valuable these 

 may be in questions concerning the relations of heat to growth. 



We cannot close this chapter without touching upon two valuable results of 

 phtBnological observations, although only in passing. The following tables gives 

 first of all a view of the retardation of vegetative development with increasing 

 latitudes in Europe in the spring. 



Comparisons with Lesina in the Adriatic Sea, 43^ 11' Nor. Lat., 16° Ifif East Long. 



As the starting-point in the comparison we choose the Island of Lesina off the 

 Dalmatian coast, because there the climatic conditions lie midway between those of 

 places situated in the same latitude in Western Oceanic and in Eastern Continental 

 Eui'ope. The stations of observation, situated not more than 300 metres above the 

 sea-level, which are here compared with Lesina, have been arranged in three columns 

 — a western between and 10 meridian, a central between 10 and 30, and an eastern 

 between 30 and 45. Reviewing the retardation due to the increasing latitude with 

 regard to Lesina, we have the interesting result that the retardation in the column 

 of the eastern continental stations is from two to three weeks more than in that of 

 the western column. Thus, when in Paris many .spring plants are in full bloom, 

 vegetation on the Russian steppes (Sarepta), at the same latitude, is still deep in 

 winter slumber, and does not reach the same stage until 23 days later. 



In a second small table inserted on next page, very remarkable results are given 

 with respect to the blossoming of the same species in Western Europe and in 

 Eastern North America. 



Here those American and European stations are placed side by side iu which 

 the blossoming of the same species occurs simultaneously, and hence the comparison 

 shows tliat the geographical position of these places differs by about 8-10 degrees 

 of latitude; so that, for example, in New York (which has the same latitude as 



