Value of gross estate includes transfers with retention of life estate or power of appointment

The value of the gross estate shall include the value of all property, to the extent of any interest therein of which the decedent has at any time made a transfer, except in the case of a bona fide sale for an adequate and full consideration in money or money's worth, by trust or otherwise, under which he has retained for his life or for any period not ascertainable without reference to his death or for any period which does not in fact end before his death the possession or enjoyment of, or the right to the income from, the property, or the right, either alone or in conjunction with any person, to designate the persons who shall possess or enjoy the property or the income therefrom.