A curious custom analogous to this of serving up hog-flesh as an expiatory offering to the spirits to whom the graveyard and its trees are sacred is to be found in Roman literature. "Cato," as Dr. Tylor reminds us,[196] "instructs the woodman how to gain indemnity for thinning a holy grove; he must offer a hog in sacrifice with this prayer, 'Be thou god or goddess to whom this grove is sacred, permit me, by the expiation of this pig, and in order to restrain the overgrowth of this wood, _etc., etc._'" The two customs are not true parallels, however, for the Chinese offers his sacrifice to the spirits of his ancestors as an atonement for the offence of cutting trees which he normally regards as the inviolable property of the dead or as associated with them in some mysterious way; whereas the Roman offered his sacrifice to a grove which was in itself sacred as being the abode of gods or dryads. We shall see later on[197] that tree-worship still finds a place in the Chinese religious system and is not extinct even in Weihaiwei, but it would be a mistake to regard the veneration shown for the trees of a family graveyard as evidence of such worship. Even if the custom of planting a graveyard with trees had in remote times a common origin with tree-worship (which is at least doubtful) there is no evidence whatever to support the view that graveyard trees are regarded as sacred in themselves at the present time. An obvious reason for planting trees in a graveyard would seem to be that it facilitated the protection of the graves from the encroachments of the plough; but the custom is more probably derived from the ancient superstition that certain trees communicate their preservative qualities to the human remains that lie below them or impart a kind of vitality or vigour to the spirits of the dead.