The kakemono, or hanging scroll, is the form in which Japanese paintings are usually mounted. It takes the place of the framed picture of Europe; but the number of kakemonos displayed in any single room is limited to one, a pair, or a set of three. Custom has moreover fixed om the tokonoma, or alcove, as the only part of the room in which these scrolls shall be hung, and prescribes rigid rules for the dimensions and other details of the mounting.
The invention of this method of showing off pictures and preserving them-for when not displayed, the kakemono is always tightly rolled up and stored away-goes back to very early Chinese days. Sometimes the kakemono contains, instead of a picture, some valued specimen of calligraphy. For Far-Eastern painting is a sort of writing, and the writing a sort of painting, and calligraphic skill is no less esteemed than skill in the painter's art.
The gaku is another Japanese method of mounting pictures, which more closely resembles the framed picture of Europe, but occupies quite a subsidiary place.
Book recommended - Anderson Pictorial Arts of Japan, Part I. pp. 116-120, where every detail of the mounting is explained.