3Where the value of any trees or underwood has been left out of account in determining the value transferred on the death of any person and tax is chargeable under paragraph 2 above on a disposal of the trees or underwood, it shall be charged on the following amount, namely.—
(a)if the disposal is a sale for full consideration in money or money's worth, on the net proceeds of the sale ; and
(b)in any other case, on the net value, at the time of the disposal, of the trees or underwood ;
and at the rate or rates at which it would have been chargeable on that death if that amount, and any amount on which tax was previously chargeable under that paragraph in relation to the death, had been included in the value transferred on death and the amount on which the tax is chargeable had formed the highest part of that value.