With the very reasonable assumption that our native chestnut is doomed to virtual extinction it is well to consider in time if it can be replaced as a timber and nut-producing tree by other chestnut species or combinations of species less subject to injury by this disease-producing organism. The Endothia fungus, as a destructive parasite, is apparently confined to the chestnut, rarely if ever harmfully affecting genera even as closely allied as the oak (Quercus) or Castanopsis. Of the various species of chestnut or Castanea those native to Japan and Central China appear most resistant, probably having been for ages accustomed to the presence of the fungus, while the European chestnut, _Castanea sativa_, our native _C. Americana_, and our chinquapin, fall easy victims when exposed to infection. Of the Asiatic forms _Castanea crenata_ of Japan and Eastern China and _C. molissima_ of the interior are most promising in this respect, though the latter is still an almost unknown quantity as regards cultivation in this country.
_Castanea crenata_, commonly known as Japan chestnut, in its more typical forms is highly resistant, so seldom showing material injury that, for practical purposes, it may be regarded as immune. Japan chestnut seedlings raised from nuts grown in proximity to our native chestnut and exposed to the influence of its pollen are at times more seriously affected, but are rarely destroyed by the bark disease. The Japan chestnut is of comparatively low growth, of small value for timber purposes, but as a nut-producer is very fruitful and precocious, bearing great crops at an early age. The nuts are often very large but usually of poor quality. The species, however, proves quite plastic in the hands of the plant breeder, being readily modified in the directions most desired by the ordinary methods of cross-pollination and selection. It freely hybridizes with all other chestnut species and varieties that have been tried, and forms the basis of the most hopeful work in breeding for disease-resistance that has yet been attempted.
_Castanea molissima_ is of much taller growth and bears nuts of moderate size, but of really good quality in the types that have reached this country. It can be infected by _Endothia parasitica_ but the disease progresses slowly and in some instances results in little harm. The species has been so recently established in America that practically nothing is known of its breeding capabilities, but if its disease-resistance under our climatic conditions is assured it would appear most hopeful material for replacing our vanishing native species. Explorers report there is a still more promising chestnut in China, reaching nearly 100 feet in height under forest conditions, but it has not yet been secured for trial in this country.