This brings us to the two crucial questions in the case, which are whether in the case of each settlement, each amount of income received by a beneficiary under an exercise of that power of the trustees which arose upon the settlor's death was property to which the recipient became beneficially entitled "by reason of" the settlement; and, if so, whether the recipient became beneficially entitled to that income "upon the death" of the settlor within the meaning of s. 4. Of course there were three links in the recipient's chain of title to each amount, the settlement, the death of the settlor and the decision of the trustees, and the amount passed to the recipient by their conjoint effect. But, as has often been held with respect to special powers of appointment, when property passes under an exercise of such a power, it is the creation of the power, and not the exercise of it, by reason of which the property is taken: Muir or Williams v. Muir [1] ; In re Dowie's Will Trusts; Barlas v. Pennefather [2] ; In re Batty; Public Trustee v. Bell [3] ; and accordingly it is the instrument conferring the power which is properly to be called the disposition: cf. In re Hoff; Carnley v. Hoff [4] . In the present cases, each exercise of the trustees' power to apply income after the settlor's death takes effect, to adapt Lord Romer's language [5] , as if the settlor had left a blank in the settlement which the trustees fill up for her; and the result of their filling it up in relation to a particular amount of income is the divesting of the antecedently existing interests in that amount and the substitution of an absolute interest therein in favour of the selected recipient. The important point is that the exercise of the trustees' power is, so to speak, to be read into the settlement, so that the income to which the exercise relates must be considered to pass as if the settlement had actually provided that after the settlor's death that sum of income should be paid or applied to or for the benefit of the chosen beneficiary. So considered, the recipient's beneficial title to that income arises "by reason of" the settlement, and arises upon the death of the settlor, not immediately but after an interval, not certainly but contingently, not originally but by way of substitutive limitation; and the recipient is the "successor", being the person entitled to the succession at the date when it becomes an interest in possession: Duke of Northumberland v. Attorney-General [6] .