The amount on which tax is charged under section 126 above on a disposal of trees or underwood shall be—
if the disposal is a sale for full consideration in money or money's worth, an amount equal to the net proceeds of the sale, and
in any other case, an amount equal to the net value of the trees or underwood at the time of the disposal.
Where, if the value of the trees or underwood had not been left out of account in determining the value transferred on the death of the person in question—
it would have been taken into account in determining the value of any relevant business property for the purposes of relief under Chapter I of this Part of this Act in relation to the transfer of value made on his death, or
it would have been so taken into account if this Act had then been in force,
the amount on which tax is charged under section 126 above shall be reduced by 50 per cent.