The only remaining question is whether the son's right to accept the offer, and by so doing to acquire the beneficial title to the half-shares subject to payment of the price fixed in the wills, must of necessity be exercised, if at all, within the same period of twenty-one years. The time primarily prescribed by the wills for notifying acceptance was one calendar month, and clearly that must expire within the period. The trustees were empowered to extend the time, without any limit being expressly set to their discretion in this regard; but we need not consider whether there is to be implied a limit which restrains within perpetuity limits the maximum possible period for acceptance. For if no such limit should be implied it is the power of extension that offends the rule against perpetuities, since it would enable the trustees, if it were valid, to give the son a right, over and above that which the will by itself gave him, to take the half-shares of "Springbanks" at the fixed price, and to do so after the perpetuity period. It is the power of extension, therefore, and not the whole benefit of the proviso, which the rule against remoteness of vesting would destroy if that power should be understood as subject to no limit of time: cf. In re Raphael [1] .