INTRODUCTION. 



of which are in the British Isles) for comparison or further use in any- 

 other way by the reader ; " and the " Scheme " is the one which he thinks, 

 after forty years' study of the subject, is the most suitable for general 

 adoption. The Chart is constructed from the blossoming of the spring 

 flowers included in the Scheme, an alphabetical list of the time of flower- 

 ing of which at the various stations is given in Dr. Hoffman's pamphlet. 

 The " Scheme " is arranged according to the calendar, and I have added 

 to the table, for the purpose of comparison, the corresponding observa- 

 tions made at Marlborough, and at Swaffham in Norfolk. Dr. Hoff- 

 • mann's Scheme comprises fewer plants, but a greater variety of vegetation- 

 phases, than that of the Phenological Committee, and perhaps on this 

 account will be more, acceptable to many persons. The plants it em- 

 braces, moreover, are, with the exception of the Tartarian honeysuckle, 

 the quince, and the vine (growing out of doors), common and familiar 

 objects to almost everybody in this country, as well as on the Continent ; 

 and observations made on them are therefore less liable to error, than 

 when made on plants which demand some botanical knowledge for their 

 identification. The difficulty and uncertainty on this head is much felt 

 by the Phenological Committee, and to avoid mistakes observers are 

 required to furnish specimens of the plants with their reports. Dr. Hoff- 

 mann's list of plants and trees is introduced in the pages of the Diary in 

 brackets for the use of those persons who may prefer his limited scheme 

 to the more comprehensive one of the Committee, 



The following is Dr. Hoffmann's summary of the most important 

 results of his work : — 



1. Since the mean temperature (for a week or month) represents only 

 a fragment of the temperature of the year, while a vegetation-phase must 

 include also the effect of the temperature of the preceding months from 

 the commencement of the period of vegetation, no coincidence between 

 the two can be expected ; and the less so since the mean temperatures 

 are observed in the shade, while our plants grow in sunshine.' 



2. The retardation towards the North of the blossoming of spring, 

 flowering plants is at once perceptible and easily understood. Summer- 



" flowering plants are retarded much less, since a compensation is afforded 

 by the greater length of the day as you go northwards. The value of this 

 fact for the possibility of the development of fruit is evident. 



3. Advancing from the West towards the East, in the same latitude {e.g. 

 Giessen, about 50°) and the same altitude, the blossoming and opening of 



' The accumulated temperature in the sun can be easily calculated from the data 

 given in the Diary, but the difficulties of ascertaining the sun temperature under all the 

 conditions of plant-life are so numerous that little confidence can be placed in this 

 method, and it has not been accepted, notwithstanding Dr. Hoffmann's persistent 

 advocacy of it. 



