because the separate bodies or grains, which before
belonged to one or the other of you in severalty, have by
consent on both sides been made your joint property. If,
however, the mixture was accidental, or if Titius mixed the
two parcels of corn without your consent, they do not belong
to you in common, because the separate grains remain distinct,
and their substance is unaltered; and in such cases the corn
no more becomes common property than does a flock formed
by the accidental mixture of Titius's sheep with yours. But if
either of you keeps the whole of the mixed corn, the other
can bring a real action for the recovery of such part of it as
belongs to him, it being part of the province of the judge to
determine the quality of the wheat which belonged to each.
29 If a man builds upon his own ground with another's materials,
the building is deemed to be his property, for buildings become
a part of the ground on which they stand. And yet he who
was owner of the materials does not cease to own them, but
he cannot bring a real action for their recovery, or sue for their
production, by reason of a clause in the Twelve Tables pro-
viding that no one shall be compelled to take out of his house
materials (tignum), even though they belong to another,
which have once been built into it, but that double their value
may be recovered by the action called ‘de tigno iniuncto.’ The
term tignum includes every kind of material employed in building,
and the object of this provision is to avoid the necessity of having
buildings pulled down; but if through some cause or other they
should be destroyed, the owner of the materials, unless he has
already sued for double value, may bring a real action for re-
covery, or a personal action for production. 30 On the other
hand, if one man builds a house on another's land with his own