82 INFLUENCE OF TEMPERATURE ON THE PROGRESS OF VEGETATION. 
These two tables show the average date, and also the earliest 
and latest dates recorded for the first flowering of the plants 
named, and for the occurrence of the other phenomena. 
Out of the nineteen plants which I have selected as having 
been most regularly observed, only two have a note in each of 
the ten years, some of the others having been unobserved in as 
many as four years. This has, of course, led to some inaccuracy 
in the dates given for the average time of flowering, but I have 
corrected this in some measure by adding or subtracting a day or 
two where no observation was taken in an exceptional year ; 
however, when all precautions have been taken, a considerable 
element of error must enter into observations of this nature, so 
that the dates and results must be considered as approximate only. 
The observations for 1882, 1883, 1884, 1885, and 1887 are 
very full and, I think, reliable; in 1878, 1879, 1880, and 1881 
the observations are few and not always to be relied on, being 
probably rather behind the real dates. The observations in 1886 
were few, and as the number of observers was small, they are 
probably slightly behind the real dates. 
With regard to the second table, I do not consider that the 
observations contained in it have so much value as those in the 
first table, as on comparing the results obtained I have found 
them very irregular and inconsistent. This irregularity is no 
doubt caused by the appearance of birds and insects, especially 
the former, being affected more by temporary causes, such as an 
occasional warm or sunny day, than by the general weather of the 
season. 
The principal point I have considered in all these observations 
is their bearing on the question of the effect of temperature on 
plant life. To illustrate this relation I have prepared the fol- 
lowing table, which shows the mean temperature of the first four 
months in each of the ten years, and the number of degrees each 
was above or below the average of the ten years; side by side 
with the number of days each year was before or behind the 
average in dates of flowering of the plants given in Table I :— 
