In all of these countries there has been an extensive general use of materials other than wood for building purposes and very many of the substitutes for lumber are products grown on the cultivated fields. The use of rice straw for roofing, as seen in the Hakone village, Fig. 8, is very general throughout the rice growing districts, and even the sides of houses may be similarly thatched, as was observed in the Canton delta region, such a construction being warm for winter and cool for summer. The life of these thatched roofs, however, is short and they must be renewed as often as every three to five years but the old straw is highly prized as fertilizer for the fields on which it is grown, or it may serve as fuel, the ashes only going to the fields. Burned clay tile, especially for the cities and public buildings, are very extensively used for roofing, clay being abundant and near at hand. In Chihli and in Manchuria millet and sorghum stems, used alone or plastered, as in Fig. 88, with a mud mortar, sometimes mixed with lime, cover the roofs of vast numbers of the dwellings outside the larger cities. At Chiao Tou in Manchuria we saw the building of the thatched millet roofs and the use of kaoliang stems as lumber. Rafters were set in the usual way and covered with a layer about two inches thick of the long kaoliang stems stripped of their leaves and tops. These were tied together and to the rafters with twine, thus forming a sort of matting. A layer of thin clay mortar was then spread over the surface and well trowelled until it began to show on the under side. Over this was applied a thatch of small millet stems bound in bundles eight inches thick, cut square across the butts to eighteen inches in length. They were dipped in water and laid in courses after the manner of shingles but the butts of the stems are driven forward to a slope which obliterates the shoulder, making the courses invisible. In the better houses this thatching may be plastered with earth mortar or with an earth-lime mortar, which is less liable to wash in heavy rain. The walls of the house we saw building were also sided with the long, large kaoliang stems. An ordinary frame with posts and girts about three feet apart had been erected, on sills and with plates carrying the roof. Standing vertically against the girts and tied to them, forming a close layer, were the kaoliang stems. These were plastered outside and in with a layer of thin earth mortar. A similar layer of stems, set up on the inside of the girts and similarly plastered, formed the inner face of the wall of the house, leaving dead air spaces between the girts.