Connected with this branch of our subject is the method of storing corn. Some persons recommend that granaries should be built for the purpose at considerable expense, the walls being made of brick, and not less than three[600] feet thick; the corn, they say, should be let in from above, the air being carefully excluded, and no windows allowed. Others, again, say that the granary should have an aspect in no direction but the north-east or north, and that the walls should be built without lime, that substance being extremely injurious[601] to corn; as to what we find recommended in reference to amurca of olives, we have already mentioned it on a former[602] occasion. In some places they build their granaries of wood, and upon pillars,[603] thinking it the best plan to leave access for the air on every side, and from below even. Some persons think, however, that the grain diminishes in bulk if laid on a floor above the level of the ground, and that it is liable to ferment beneath a roof of tiles. Many persons say, too, that the grain should never be stirred up to air[604] it, as the weevil is never known to penetrate beyond four fingers in depth; consequently, beyond that depth there is no danger. According to Columella,[605] the west wind is beneficial to grain, a thing that surprises me, as that wind is generally a very parching[606] one. Some persons recommend that, before housing the corn, a bramble-frog should be hung up by one of the hind legs at the threshold of the granary. To me it appears that the most important precaution of all is to house the grain at the proper time; for if it is unripe when cut, and not sufficiently firm, or if it is got in in a heated state, it follows of necessity that noxious insects will breed in it. There are several causes which contribute to the preservation of grain; the outer[607] coats in some kinds are more numerous, as in millet, for instance; the juices are of an oleaginous nature,[608] and so supply ample moisture, as in sesame, for example; while in other kinds, again, they are naturally bitter,[609] as in the lupine and the chicheling vetch. It is in wheat more particularly that insects breed, as it is apt to heat from the density of its juices, and the grain is covered with a thick bran. In barley the chaff is thinner, and the same is the case with all the leguminous seeds: it is for this reason that they do not ordinarily breed insects. The bean, however, is covered with a coat of a thicker substance; and hence it is that it ferments. Some persons sprinkle wheat, in order to make it keep the longer, with amurca[610] of olives, a quadrantal to a thousand modii: others, again, with powdered Chalcidian or Carian chalk, or with worm-wood.[611] There is a certain earth found at Olynthus, and at Cerinthus, in Eubœa, which prevents grain from spoiling. If garnered in the ear, grain is hardly ever found to suffer any injury.