It is generally recognized that a limitation of an estate to vest in the future is perfectly valid, although the vesting may occur at a time more remote than that fixed by the rule, if it must occur during the continuance of an estate in fee tail created by the same instrument, or imme" diately on the termination of such estate.38 The basis asserted for this view is that the tenant in fee tail may at any time, by a common recovery or by a conveyance in fee simple, as provided by statute, destroy the limitation, so that it is in effect nonexistent as to him.39 In such a case the limitation, being exclusively in favor of, and in the absolute control of, one who has an existing estate in the land, may be regarded as a mere appurtenance to such estate for the purpose of the rule. It no more acts as a clog on the alienation or development of the property than does the estate itself.

The validity of a covenant by a lessor for perpetual renewal is generally recognized,40 and this is sometimes

36. As indicated in Winsor v. Mills, 157 Mass. 362, 32 N. E. 352.

37. See Gray, Perpetuities, Sec.Sec. 121c, 121f.

38. Lewis, Perpetuity, 664; Gray, Perpetuities, Sec.Sec. 443-453; Marsden, Perpetuities, c. 7; 1 Jarman, Wills, 217; Cole v. Se-well, 4 Dru. & War. 1, 2 H. L. Cas. 186; Goodwin v. Clark, 1 Lev. 35, Nicholls v. Sheffield, 2 Browne, Ch. 215, Bristow v. Boothby, 2 Sim. & S. 465, Barber v. Pittsburg, Ft. W. & C. R. Co., 166 U. S. 83, 41 L. Ed. 925.

39. Consequently such a limitation is void in jurisdictions where the tenant in tail has no power to convey the fee, the reason for the doctrine being nonexistent. St. John v. Dann, 66 Conn. 401, 34 Atl. 110.

40. Hare v. Burges, 4 Kay & J. 45; Muller v. Trafford (1901) 1 Ch. 54; Pollock v. Booth, Ir. Rep. 9 Eq. 229; Page v. Estey, 54 Me. 319; Banks v. Haskey, 45 Md. 20.7; Blackmore v. Boardman, 28 Mo. 420; Hoff v. Royal Metal Furniture Co., 117 App. Div. 884, 103 N. Y. Supp. 371, 189 N. Y. 555, 82 N. E. 1128; Creighton v. McKee, 2 referred to as involving an exception to the "Rule against Perpetuities.41 It involves such an exception, however, it is submitted, only in the sense that a limitation subject to destruction by a tenant in tail involves an exception to the rule, that is, the exercise of the right of renewal being in the absolute control of the tenant of the estate for years, it may be regarded as a mere appurtenance thereto, and has no such independent existence as to involve any clog on the title, other than such as exists by reason of the estate for years itself.42 It would seem that, on the same theory, an option of purchase in the lessee, though exercisable at a time beyond the limits of the rule, may be regarded as valid, it being absolutely in the control of the owner of an existing estate therein, and so not constituting a clog on the title independent of such estate.43 A like reason exists for the validity of a right of re-entry for breach of a condition inserted in a lease for years, however remote may be the possible time of its exercise, even in a jurisdiction where, as in England, a condition of reentry in connection with a fee simple estate is invalid.44 The condition or right of re-entry can be exercised only by the owner of an existing estate in the land, the estate in reversion, and consequently no more involves a clog upon the title than does the reversion itself, to which it is appurtenant.