78 



J. HOPKINSON" PHENOLOGICAL PHENOMEN'A 



Confining our remarks to the plants, and excluding the ivy, 

 flowering in September, it will be found that out of 38 species of 

 which the time of flowering has been observed in all the six years, to 

 which may be added 10 with only one year out of the six without a re- 

 cord, all of which 48 species come into flower as a rule during the six 

 months February to July, 22 came out in 1881 earlier than the pre- 

 vious mean date (1876-80), 8 later, and 18 within three days of the 

 previous mean, showing that in 1881 vegetation was generally in a 

 rather more forward state than the average of the previous five years. 



It has before been shown that in 1880 vegetation was more than 

 eight days more forward than the average of the four previous 

 years. A similar analysis of all the dates in 1881 of the 48 species 

 mentioned shows an extent of forwardness over the mean of the 

 previous five years of only 3 days, or more exactly 3"1. 



The relation of each of these six years to the mean of the whole 

 is shown in the accompanying diagram. The 48 selected species 

 which come into flower from February to July, as a rule, being 

 grouped into twelve sets of four each, each set will represent a 

 duration of time of about a fortnight. The mean for the six years 

 of each of these groups being calculated, and also the mean for each 

 year of the six, the difference in each year from the mean of the 

 whole period is laid down on the diagram, if earlier above the 

 centre line and if later below it, each horizontal line representing 

 four days' variation from the mean. The points thus found are then 

 connected by a dotted line, which therefore shows approximately 

 the state of vegetation for about every two weeks during six months 

 each year in reference to the mean of the six years. 



1876 



1877 



1878 



1879 



1880 



1881 



The number of species from the observation of which these means 

 are derived being very small, the line thus shown is necessarily 

 irregular, and a nearer approach to the actual state of vegetation 

 may be arrived at by titking the mean date of flowering of every 

 eight species instead of that of every four. In the same diagram 

 the result of this is shown in the unbroken line, which therefore 

 represents tlie extent of backwardness or forwardness of each 

 month from February to July. It will be seen that in February 

 1876 and April 1879 plants were very late in flowering, that in 

 February 1877 and March 1878 they were very early, and that in 

 April and July 1876, March and April 1877, February and March 

 1880, and March and April 1881 they were in flower at about the 

 average date for the whole period. 



