174 AGRICULTURE AND FORESTRY. 



wards, the blossom-spikes are developed. Its blossoms are odour- 

 less, of a red colour, and very similar to several other kinds of 

 Polygonum in their appearance and structure. They come- forth 

 in August and September, and the harvest generally takes place 

 before they are fully developed. Chemical investigation has shown 

 that the Indigochromogen, Indican, is confined to the leaf-paren- 

 chym, in cells, and that the stems and blossoms are devoid of it.^ 

 The method of cultivating and handling the plant is in accord- 

 ance with" this fact. 



The dyer's knotweed is by far the most important Japanese dye- 

 plant. It is from it that the indigo is obtained which is so generally 

 used for colouring cotton and hempen garments. It is cultivated, 

 therefore, over a wide stretch of territory, being found in the plains 

 and valleys of nearly all districts south of Yezo. In planting it, 

 the seed is seldom sown directly in the fields, but mostly in beds, 

 from which shoots are taken and set out in rows. These young 

 plants are 12 to 15 cm. high. If the seed is sown in early spring, 

 and strong fertilizers, such as fish-guano and oil-cakes, are re- 

 peatedly applied, they attain this height within two months, and 

 are then ready to be transplanted. In 60 to 70 days more — about 

 the end of July or the beginning of August — the chief harvest 

 commences, to be followed by a second crop, as in the case of 

 clover. And an Ai-plantation, seen from a distance, looks like a 

 clover-field before its heads have burst. When the stalks are about 

 30 cm. high they are cut off with the sickle, close above the ground. 

 Their upper parts, which have the most leaves, are justly considered 

 of the greatest value ; and these, with the leaves, are cut off from 

 the lower stalks, which are dried and then burned for the sake of 

 a highly-prized kind of ashes (Ai-no-hai) thus obtained. The 

 leaves, however, are spread in the sun to dry before the house, 

 frequently on the bare ground, so that the dust of the streets is 

 not excluded. They become thus a dull, dark green, and in this 

 condition are put away in straw-rope sacks for further treatment. 

 This takes 70 to 80 days, differing very considerably in this 

 and other respects from the short soaking-processes by which 

 indigo is obtained elsewhere from other plants. It is a sort of 

 fermentation, and has to be conducted with great attention and 

 skill. The leaves, after being sprinkled with a certain quantity 

 of water, and thoroughly mixed with it, are spread out and left 

 3 to 5 days, under a cover of mats. The process is repeated 19 to 

 20 times altogether, and finally the leaves are put into a wooden 

 mortar. Here in two day's time they are worked into a doughy 

 mass of a dark blue colour. From this balls are made, from the 



^ Schunk: " On Indian Blue from Polygonum tinctorium and other Plants." 

 "Memoirs of the Lit. and Phil. Soc, Manchester." Vol. vi. (3 Series), pp. 218- 

 234. 



See also Fliickiger's Report in the " Botanisches Jahresbericht of Just," VII. 

 2, p. 343. 1879. 



