180 



KNOWLEDGE. 



May, 1913. 



BOTANY. 



By Professor F. Cavers, D.Sc, F.L.S. 



VEGETATION OF JAPAN.— Mr. H. Takeda gives, in the 

 February number of The New Phytologist, an extremely 

 interesting and readable account of the geography, climate, 

 and vegetation of Japan, which has well been termed the 

 " Britain of the East " — in fact, the author begins with the 

 almost inevitable comparison between the geographical 

 positions of Japan on the Asiatic coast and of Britain on that 

 of Europe. Apart from the geographical resemblance and the 

 existence of a warm current comparable with the Gulf Stream, 

 however, the climate and the vegetation show striking differ- 

 ences, as might, indeed, be expected. 



The Japanese Empire consists, from north to south, of the 

 Kurile islands, the southern half of the Saghalien, Yezo, the 

 main island known to the Japanese as Honto, though by others 

 often called Nippon, Shikoku, Kyushu, the Loochoos, Formosa, 

 and the Pescadores ; these islands stretch diagonally from 

 52° to 21° N. Lat., and lie between 120° and 156° E. Long. 

 This area was in 1910 increased by the annexation of Corea, 

 hence the Empire has now about the same area (over two 

 hundred and fifty-six thousand square miles) as Austria- 

 Hungary, and the perflation (over sixty-three millions) is 

 nearly equal to that of Germany. 



A warm current, the " Kuroshio," similar to the Gulf 

 Stream, arises between Luzon and Formosa, and flows along 

 the southern Loochoos to the southern end of Kyushu where 

 it divides into two ; the main stream bends northward and 

 flows along the south-east coast of Kyushu, Shikoku, and 

 Honto, while the smaller branch washes the west of Kyushu 

 and the Goto group and runs up to the Sea of Japan through 

 the strait of Tsushima or Krusenstern. The cold currents in 

 the North Pacific which affect the climate of Japan arise in 

 the Sea of Okhotsk and in the Behring Sea ; the most impor- 

 tant of these, the Kurile Stream, flows southwards along 

 Kamtschatka, turns towards the Kuriles and washes the 

 whole length of the island chain, and then runs chiefly along 

 the east coast of Yezo to 39° N. Lat., where the above- 

 mentioned main stream of the warm current bends away into 

 the Pacific Ocean ; the water of this Kurile Stream is very 

 cold, and even in summer its temperature does not rise above 

 5°C. 



These warm and cold currents exert great influence on the 

 distribution of seaweeds ; this is clearly seen on the east 

 coast of Japan, the thirty-ninth degree being the separating 

 point of two different alga floras. On the west coast, however, 

 the course of the currents is more complicated, hence the 

 elements of different floras appear somewhat intermixed. The 

 strand flora is similarly affected, the northern elements being 

 distributed in the localities touched by the cold currents. 

 For instance, Mertensia maritima (with stouter stem and 

 larger flowers than the type in Europe and America) has a 

 wide distribution from the Behring Sea to 38° N. Lat. in 

 Okhotsk, Manchuria, North Corea, and Honto; Glaux mari- 

 tima., another arctic plant, is distributed mainly from Yezo 

 northward, but also occurs in a locality on the west coast of 

 Honto, whither it was probably carried by the cold currents ; 

 Plantago camtschatica is another plant found in localities 

 visited by these currents. As the warm current comes into 

 direct contact with the southern parts of Kyushu, Shikoku, 

 and Kii, various sub-tropical plants are found in these places — 

 Rhizophora mucronata, Senecio scandens, Ipomaea 

 pescaprae, Pteris Wallichiana, Asplenium Nidus, and so 

 on ; Statice japonica, mainly distributed in south-west Japan, 

 also occurs on the east coast as far north as 38° N. Lat. 



The islands of Japan are all mountainous, some of the 

 smaller islands consisting simply of one or more volcanoes, 

 and most of the high mountains are densely clad with 

 luxuriant vegetation from foot to summit, often so densely 

 that the mountain forests are almost impenetrable. The 

 great chains in Central Japan, forming the backbone of Honto, 

 rise in places to three thousand five hundred metres ; there 

 are no glaciers, though traces of earlier glaciation have been 

 noted, but considerable neve is present on some of the 



mountains. As the mountainous nature of the country would 

 suggest, Japan is naturally very rich in water ; a dense net- 

 work of rivers, torrents, and lakes is seen almost everywhere. 

 The rivers are usually short and their gradient steep, causing 

 frequent floods ; in late spring, when the snow begins to melt, 

 or when in summer the continuous rain carried by the south- 

 west monsoon falls in torrents, the mountain streams are 

 converted into raging floods. 



Owing to the extension over thirty degrees of latitude and 

 the great variety in physiography, the climate is very varied ; 

 it is much influenced by that of the neighbouring countries 

 and modified by the warm and cold currents above mentioned. 

 The climate of the region from Formosa northward to the 

 mouth of the Amur River is controlled by the monsoons, formed 

 by the warm damp south wind in summer and the cold north 

 winds in winter ; the Loochoos, down to Formosa, are sub- 

 tropical and have practically no winter ; while the Kuriles, 

 south Saghalien, and parts of Yezo have the climate of Nova 

 Scotia or Iceland. In the winter drifting ice is carried by 

 currents and wind in the Kuriles and blocks up harbours from 

 November to April ; on the northernmost islands, not until 

 June does the snow disappear and vegetation awaken. The 

 rainfall is high (about one hundred and fifty centimetres a 

 year in Tokyo), especially in summer, when the air is very 

 damp, except in Yezo and the Kuriles which are not affected 

 by the monsoon ; the winter is dry and fine ; the annual 

 temperature range is considerable — in Tokyo the mean 

 temperature is 13°-8 C, maximum 36°-6, minimum 9°-2. 



The vegetation is, naturally, well developed, varied and 

 abundant, with about four thousand five hundred cryptogamic 

 and six thousand phanerogamic species — apart from the floras 

 of South Saghalien (three hundred species of vascular plants 

 described) and Corea (two thousand two hundred species, of 

 which about two hundred are endemic). Though Japan is 

 surrounded by seas, in the west it is closely connected with 

 Manchuria through Corea, in the north it reaches Kamtschatka 

 by the Kurile islands, and Alaska through the Aleutian 

 islands, and it also has a connection with Amurland through 

 Saghalien ; on the other hand, the Loochoos and Formosa 

 join it to South China, the Philippines and the East Indian 

 islands. Hence, except on the eastern side, it is closely con- 

 nected with other countries, the floras of which show many 

 signs of close relationship with that of Japan, which was 

 probably connected with the mainland of Asia until a com- 

 paratively recent period. Plants indigenous in Eastern Asia 

 are also found in Japan, and teeth and bones of the mammoth 

 have been found in various parts of the country. 



The main characters of the Japanese flora are (1) the 

 abundance of species and varieties, (2) the presence of 

 numerous endemic species, (3) the remarkably high proportion 

 of woody plants, (4) the presence of tropical and sub-tropical 

 plants throughout the country. Even in Yezo, the large 

 island of North Japan, are found many representatives of 

 southern floras (Picrasma, Vitex, Rhus, Hydrangea, 

 Aralia, Magnolia, and so on) growing together with 

 representatives of the cold flora ; in the northern parts of Honto 

 Aesculus, Zanthoxylon, Ardisia, Elaeagnus, Smilax, and 

 Camellia are often seen. The same or closely allied species 

 have been found in the Tertiary strata of the north of Eastern 

 Asia. Probably in the middle of the Tertiary period, even 

 Saghalien had a much warmer climate, for at that time 

 Ginkgo, Biota, and Sequoia grew there. When, towards the 

 close of the Tertiary, the greater part of the northern 

 Hemisphere was covered with ice, the main island of Japan 

 seems to have suffered very little. Probably since the end of 

 the glacial period and the change of climate in the middle 

 diluvial age, Japan has maintained a fairly warm temperature 

 enabling many plants of warmer climates to survive, while in 

 Saghalien the temperature has been very low so that this 

 island is unfavourable to plants of the warm temperate region. 

 The arctic plants once compelled by the cold climate of the 

 glacial period to come southward were consequently left 

 behind when the climate became warmer, but only persist on 

 the summits of the high mountains. 



Starting with the flora established in the Tertiary period, the 

 migration of arctic plants towards the south and of tropical 



