But such powers survive, and, after the death of one of the donees, may be executed by the survivor,203 unless the power is given to the several donees by name, showing that personal trust and confidence is imposed in them,204 and even in these cases the power may be exercised by the survivors, if coupled with an interest.205 If a power is given to executors nominatim, they may appoint under the power, though they have resigned as executors.206 Where no personal trust or confidence is imposed on the donee of a power, it may be executed by attorney;207 otherwise the donee must use his own discretion in making the appointment.208 The mere execution of an instrument may in all cases be by attorney.209 A general power may be transferred, and, when a power is given to a person and his assigns, it may be executed by his assigns in fact or in law.210