INFLUENCE OF TEMPERATURE ON THE PROGRESS OF VEGETATION. 85 
few weeks of frost have less effect in retarding them than might 
have been expected. 
Having thus stated the results obtained from a comparison of 
our recorded observations, I will make some suggestions for more 
systematic work in the future. 
The observations on birds and insects are, as I have already 
mentioned, not to be relied on as a criterion of the comparative 
forwardness of a season, so that the preference should be given to 
observations on the dates of first flowering of common plants. A 
list should be drawn up of a moderate number of common and 
well-known plants, such as those included in my first table, and 
these should be carefully noted each year by, if possible, several 
observers. 
Next, similar observations should be made of the dates of 
_leafing of our common trees. This department has been much 
neglected among us, as, in looking through our records for the 
ten years, I found only five notes of the Oak, three of the Ash, 
five of the Horse Chestnut, and of others even fewer ; the only 
tree which has been at all regularly observed is the Hawthorn, 
which was noted in each of the ten years. The principal reason 
for this neglect is, probably, the difficulty in saying when a tree 
really is in leaf, the progress being so gradual. The best plan, in 
my opinion, is to make the observation directly the leaf bud has 
burst. 
With regard to the leafing of trees, a method, which commends 
itself to me as being both simple and accurate, is to note a 
particular tree or particular trees each year, so as to get rid of 
local and individual differences. This method might also be 
applied to the flowering of trees, but could not conveniently be 
applied to herbaceous plants ; with regard to them, however, an 
analogous plan might be adopted of observing them as nearly as 
possible in the same spot each year. Careful note should in all 
cases be made of the locality of each observation, as so much 
depends on aspect, soil, and altitude. 
