34 Where, on the other hand, one man paints a picture on another's board, some think that the board belongs, by accession, to the painter, others, that the painting, however great its excellence, becomes part of the board. The former appears to us the better opinion, for it is absurd that a painting by Apelles or Parrhasius should be an accessory of a board which, in itself, is thoroughly worthless. Hence, if the owner of the board has possession of the picture, and is sued for it by the painter, who nevertheless refuses to pay the cost of the board, he will be able to repel him by the plea of fraud. If, on the other hand, the painter has possession, it follows from what has been said that the former owner of the board, [if he is to be able to sue at all], must claim it by a modified and not by a direct action; and in this case, if he refuses to pay the cost of the picture, he can be repelled by the plea of fraud, provided that the possession of the painter be in good faith; for it is clear, that if the board was stolen by the painter, or some one else, from its former owner, the latter can bring the action of theft. 35 If a man in good faith buys land from another who is not its owner, though he believed he was, or acquires it in good faith by gift or some other lawful title, natural reason directs that the fruits which he has gathered shall be his, in consideration of his care and cultivation: consequently if the owner subsequently appears and claims the land by real action, he cannot sue for fruits which the possessor has consumed. This, however, is not allowed to one who takes possession of land which to his knowledge belongs to another person, and therefore he is obliged not only to restore the land, but to make compensation for fruits even though they have been consumed. 36 A person who has a usufruct in land does not become owner of the fruits which grow thereon until he has himself gathered them; consequently fruits which, at the moment of his decease, though ripe, are yet ungathered, do not belong to his heir, but to the owner of the land. What has been said applies also in the main to the lessee of land. 37 The term 'fruits,' when used of animals, comprises their young, as well as milk, hair, and wool; thus lambs, kids, calves, and foals, belong at once, by the natural law of ownership, to the fructuary. But the term does not include the offspring of a female slave, which consequently belongs to her master; for it seemed absurd to reckon human beings as fruits, when it is for their sake that all other fruits have been provided by nature. 38 The usufructuary of a flock, as Julian held, ought to replace any of the animals which die from the young of the rest, and, if his usufruct be of land, to replace dead vines or trees; for it is his duty to cultivate according to law and use them like a careful head of a family.