44 
H. Takeda. 
from the north or north-west, where they were accustomed to a 
severe winter, migrated up the mountains until they obtained the 
necessary climatic conditions. 
Migrations must also have taken place in the post-tertiary 
period, for the great majority of the volcanoes were built up then, 
and also the irregularity of the surface of the country was to some 
extent brought about at this time. 
From the results of investigations of the tertiary fossils of 
Japan, of Amurland, and of N. America, the conclusion may be 
drawn that the present flora originated in the large common flora 
of the northern region of the Far East. Its development to its 
present condition has already been elucidated. One striking 
feature is that the flora of the N.E. part of Japan bears a close 
relationship to that of the Atlantic coast of N. America. This was 
first noticed by Asa Gray a good many years ago. He endeavoured 
to compare the two floras and showed that more that 60% of 
Japanese plants grew on the E. coast of N. America, or if not, 
were represented by closely related species, while only 37% of these 
can be seen on the W. coast. He accordingly suggested that the 
close affinity between these floras originated in the tertiary period. 
Asa Gray’s conclusion has been more and more firmly established 
as further geological evidence has accumulated, and consequently 
Engler and other geographical botanists have come to the conclusion 
that these two regions were actually connected, and had a similar 
climate and similar flora. After the glacial period many plants 
which migrated towards the south returned northwards and formed 
the foundation of the present flora of Japan, while in N. America, 
a change in climate had taken place between that of east and west. 
While in the west the climate became dry and mild and caused a 
great alteration in the flora, in the east very little change has taken 
place, and many old species have been preserved. 
It should be borne in mind, however, that the vegetation of 
Japan, except that of the northern islands, has little actual 
resemblance to that of N. America. Although the same or closely 
allied plants occur in both regions, they are not found in the same 
proportion. For instance, in Japan Tsuga forms continuous and 
almost unbroken forests of great extent on the mountain slopes, 
above 5,000 feet from sea level, while in eastern N. America this tree 
is rarely found except scattered in small groves or as single 
individuals in the deciduous forests. On the other hand, Picea and 
Abies , which in America form immense forests almost to the 
