VIIL 1. THE NECKLACE POPLAR. 249 
age year, the aspen began to flower, at Middletown, April Ist, 
the large poplar, about the 4th, and three others, on the 9th. 
Dr. Barratt has observations on the period of flowering through 
fifteen degrees of north latitude, which give three months as the 
difference in the time of beginning, or one month’s difference 
for five degrees of latitude, which is equal to six days for one 
degree ; so that spring goes northward at the rate of one degree 
in six days, or ten milesa day. This is the average for fifteen 
degrees, and would give a difference of five days between Mid- 
dletown and Boston, the difference of latitude being 48’ 12”. 
The actual difference is greater, being from six to ten days, 
showing that the advance of spring is not uniform throughout 
every part of the fifteen degrees. The difference against Boston 
is probably owing to the influence of the chilling north-east 
winds which prevail at that season of the year. 
Dr. Barratt’s conclusion is not far different from that reached 
by Dr. Bigelow,* from a comparison of the times of flowering of 
several common plants, in various parts of the United States 
and Canada, in the spring of 1817. Dr. Bigelow made a differ- 
ence of two months and a half for a difference of latitude of 13° 
45’, which would be three months for 16° 30’. Generalizations of 
this kind, to be valuable, must be cautiously made, drawn from 
the average of a large number of species, and a somewhat long 
series of years. In the data furnished by Dr. Bigelow’s corres- 
pondents, if an inference were drawn from the apple and pear 
alone, the difference in the season between Charleston and Mon- 
treal, whose difference of latitude is 12° 51’, would be only one 
month and twenty-one days; if from the flowering of the blood 
root, it would be only one month and eleven days, conclusions 
widely different from those drawn from the average of all the 
species observed. 
Sp. 5. Tse Necrrace Poptar. P. monilifera. Aiton. 
Leaves figured in Michaux, Plate 96. A leafy branch is figured by Abbott, 
Insects, Il, Plate 71, with the Kitten Moth. 
This tree has an erect or slightly bending trunk, tapering 
gradually to a height of fifty or sixty feet, and covered with a 
* See Memoirs of the American Academy, Vol. IV, p. 77. 
33 
