Studies on the geographical distribution of the weeds on paddy field in Japan.

Abstract

1) In order to obtain a fundamental knowledge for the control of weeds, the writer have investigated since 1942, under the co-operation of thirty seven plant taxonomists who live in different regions of Japan, what kinds of weeds are found on the paddy field as well as the upland field and how is their geographical distribution. 2) Japan was subdivided into 10 weather sections according to Dr. FUKUI, that is Hokkaido (B.C) Sanriku (Ej), Ryou (Ep), Hokuriku (Eq), Tozan (El), Tokai (Ek), Sanin (Fr), Setonaikai (Em), Kitakyushu (En), and Nankai (Eo), and each of these districts were investigated kinds and their abundance of weeds in paddy field. 3) The total number of species of weeds grown on paddy field in the whole region of Japan, except in Hokkaido, amounted to 186 species of 42 families. Among them, 30 species were recognized as the most noxious, 68 species as the moderately noxious and 88 species as the slightly noxious. 4) Hokkaido has considerably different kinds of weeds in the paddy field from the other part of Japan; about 73 species of weeds which are distributed in Honshu are not in found in Hokkaido, and, on the other hand, some frigid plants which are not seen in the Main Land grow on the paddy field in Hokkaido. This seemed to be due to the low temperature and the short historical period of rice growing in the district. 5) Majority kinds of weeds are more or less widely distributed throughout Japan, exclusive of Hokkaido, and weeds on the paddy field which are confined to the south-western part are only 9 kinds. 6) Among 186 species of weeds on the paddy field in Japan, only a few species are endemic to this country, majority parts of them being common to the other part of the worId, and they are considered to be originated from south-eastern Asia and southern China. 7) It is noteworthy that there are very few species of naturalized weeds on the paddy field which are distributed in a limited area, while that as many as about 80 kinds of naturalized weeds on the upland field in Japan are known to have invaded from some foreign countries in recent time.