Vll 



dahurica, var. japonica Maxim, reaches Shikotan in the southern Kuriles only a 

 few miles from northeast Hokkaido and is abundant in Saghalien where grow in 

 great plenty Abies sachalinensis Mast, and Picea jezoensis Carr. which are the 

 dominant conifers of the Hokkaido forests. 



It has been stated and the statement is rather widely accepted that the Tsugaru 

 Straits which separate northern Hondo and Hokkaido form a well-marked phytogeo- 

 graphical and zoogeographical boundary the so-called Blakiston line but so 

 far as plants are concerned this has no foundation in fact. The warm current 

 which flows up the east coast of Japan and is deflected out to sea about the lati- 

 tude of Tokyo exercises a strong influence over the climate and consequently also 

 over the flora. South of Tokyo broad-leaved evergreens are a feature of the vege- 

 tation and north of that latitude they rapidly disappear and the general appearance 

 of the forests is markedly different. No hard and fast phytogeographical bound- 

 ary exists, but such as it is it is found about latitude 36. 



The whole flora of Japan is largely endemic but is an integral part of the 

 great flora which includes that of southern Korea, has its headquarters in China 

 and extends westward to the border of the Thibetan highlands and along the 

 Himalayas to eastern Nepal. In northern Hondo and in Hokkaido are many 

 elements of the flora of continental northeast Asia which extends eastward from 

 the region of Lake Baikal. And in the same region of Japan grow a number of 

 circumpolar plants, especially members of the Ericaceae. There is some affinity 

 between the flora of Japan and that of eastern North America, but it is much less 

 strong than between the floras of the latter region and of central China. As far as 

 the conifers and taxads of Japan are concerned the affinity is certainly more with 

 western North America than with the region east of the Mississippi River. In- 

 deed, only the Hemlocks, the two Hard Pines and Picea Glehnii Mast, can be said 

 to be more nearly related to species of eastern North America than to those of 

 the Pacific slope. 



Japan is composed fundamentally of Archean rocks much overlaid with vol- 

 canic ejectamenta during different geological epochs. It is very mountainous and 

 is mainly made up of a backbone of volcanic ranges, of which many peaks are still 

 active, and narrow flanks of sedimentary rocks. In western Shinano and Hida 

 provinces in central Hondo there are granite mountains and the southern island 

 of Yaku-shima is a gigantic upthrust of the same igneous rock. There is extremely 

 little limestone in Japan and this may have much to do with its richness in conif- 

 erous trees. The rainfall varies according to latitude from about twenty-six inches 

 to one hundred and nineteen inches in a year and the number of rainy days aver- 

 ages about one hundred and fifty. The annual average amount of moisture in the 

 air is given as 80 per cent. The high humidity and abundant precipitation are very 

 favorable to the growth of coniferous plants. The climate of the greater part of 

 Japan is mild and equable; in the extreme south it is warm-temperate and in the 

 extreme north the summers are short and hot and the winters long and almost arctic 

 in severity. But in the north snow lies deep and undisturbed upon the ground from 

 December to the approach of spring in April and is an effectual protection to the 

 numerous low-growing, broad-leaved Bamboos (Sasa spp.) and such evergreen 

 shrubs as Skimmia japonica Thunb., Daphniphyllum humile Maxim., Ilex rugosa 

 Schmidt and others which form the characteristic undergrowth in the forests. 



The formation of the islands, with their high central ranges and short precipi- 

 tous swift-flowing rivers, make floods particularly prevalent and dangerous, and 

 the necessity of preserving the forest-covering of the upper mountain-slopes pro- 



