446 MR. HISAYOSHI TAKEDA ON THE 
Sakhalien formed a peninsula projecting from the Asiatic Continent, while 
Hontó had been cut off from this peninsula at an earlier period by the 
Strait of Tsugaru. Thus Tsugaru Strait forms a decided line of demar- 
cation between the fauna of Hontó and that of Yezo, and the latter 
island contains practically the same species of animals as those found on 
continental Asia. This hypothesis has been valued by zoologists, and 
the Strait of Tsugaru has consequently been called the “ Blakiston Line." 
It is quite true that the “ Blakiston Line” has some bearings on the dis- 
tribution of plants on Yezo, as it has on the fauna. However, if we closely 
examine the floras of Hontó, Yezo, the Kuriles, and of Sakhalien, we are 
unable to appreciate Blakiston’s disregard of the importance of the Strait 
of La Pérouse. As I have shown above, the flora of the Kuriles is more 
closely related to that of Hontd than to that of Sakhalien. And so is the 
flora of Yezo. So far as the botanical evidence shows, La Pérouse Strait 
is the primary line of demarcation, and Tsugaru Strait the secondary. It 
is true, as Blakiston mentions, that the Strait of La Pérouse is shallower 
than the Strait of Tsugaru; but in my opinion very little value can 
be attached to the depth or breadth of the water separating an island 
from the main land or two islands from one another, for determining the 
period when the land in question became disconnected. It would be 
astonishing if one finds that the flora of Quelpaert or Che-ju Island is 
more closely related to that of Japan than that of the Corean Peninsula *. 
As I have pointed out above, botanieally speaking, the Kurile Islands 
are closely connected with Yezo. Geographically, their southern parts 
seem to have been once in more intimate connection. As to the northern 
islands, Milne f advanced an opinion of their very recent formation. His 
hy pothesis was followed by Miyabe f, who considers that Yezo had connection 
with the Asiatic Continent only through Sakhalien. The floristic evidence, 
however, does not point that way. I have therefore been led to the con- 
clusion that the Northern Kuriles have been in existence before the Strait of 
La Pérouse was formed, and that this had some effect on the distri- 
bution of plants. It must be borne in mind that voleanie activity in the 
Northern Kuriles has not always been constructive, but also destructive, and 
that the geographical features must have varied in consequence. In order 
to arrive at a more correct calculation I should have to consider the whole 
Kurile flora, the material for which, however, I have not at present at my 
* There is no extensive phytogeographical work of this island. Its floristic relationship 
may, however, be seen to some extent in the paper “ Plant; ex insula Tschedschu,” by 
Takeda and Nakai, in Toky6 Bot. Mag. xxiii., 1909. 
T J. Milne, ‘ Evidences of the Glacial Period in Japan,” in Trans. Asiat. Soc. Japan, ix. 
(1881) pp. 53-85. 
t Miyabe, in Mem, Boston Soc. Nat. Hist. iv. (1890) p. 212. 
