402, REPORT OF THE CONFERENCE ON GENETICS. 
states that no species of plant has extended 100 miles north of its original 
limits within historic times, although seeds have been carried far north of 
the original limits by birds and other agencies; and that changements 
of form or duration are required, or periods of four or five thousand years 
are needed, for it to endure a greater degree of cold. In testing a collec- 
tion of over 500 varieties and species of ornamental trees and shrubs 
from various parts of the world, their different degrees of hardiness under 
severe climatic conditions, which meant at one time 40° Fahr. below zero 
with the ground bare of snow, led me to investigate the geographical 
range of each species. De Candolle’s law of hardiness, just quoted, 
appeared to me a satisfactory explanation of the behaviour of these 
many species of plants. 
In connection with the law just quoted it will be of interest to 
give some of the costly experience, in the prairie North-West, of our 
nurserymen and tree-planters. I will give only a few out of many 
instances. 
The box elder (Acer Negundo or Negundo aceroides) from Virginia, 
winter kills in the North-West, while the local form of the box elder 
indistinguishable from it by botanical characters, is perfectly hardy. The 
tree-planters of Manitoba have found that the box elder from several 
hundred miles south will not endure Manitoba winters, while the same 
species from their own locality, known as the Manitoba maple, is perfectly 
hardy. In Russia the box elder was once considered tender in the north ; 
it was found that their seed was gathered near St. Louis; since then seed 
from the far north has been tested and found hardy. 
The red cedar was formerly brought to the north in large quantities 
from Tennessee, which is well to the south. Northern nurserymen have 
learned that they must cultivate only the northern form of the red cedar 
to avoid total failure. ‘i 
Robert Douglas, of Illinois, found a great difference in hardiness 
between the northérn and southern forms of the black walnut. The 
former lived, the southern died, in Northern Illinois. 
They have found also that they must be careful as to the source of 
western conifers. For cultivation in the prairie North-West, the form 
from the Pacific slope of the Rocky Mountains is tender, while if gathered 
on the eastern slope of the Rockies it is hardy. 
Much more evidence might be given along the same line, all going to 
show that Nature has done this great work of acclimatising species, but 
that thousands of years are needed for the work. The converse of the 
law appears to be true, that a species cannot be extended southward to any 
ereat extent beyond its natural limits. Munson, of Texas, has found that 
the northern americana plums are winter-killed in Texas, because the 
buds start prematurely at the first warm spell in mid-winter. In Russia 
a similar tendency has been noticed with the Siberian larch when brought 
into Southern Russia. 
It will be noted that this law applies only to wooded plants that must 
endure the winter, not to annual plants such as Indian corn or maize. - 
This species has been advanced many hundreds of miles northward by 
shortening the season. In what is considered its native home, in the 
tropical or semi-tropical regions of South and Central America, it takes 
