This section is from the book "The Law Of Real Property and Other Interests In Land", by Herbert Thorn Dike Tiffany. Also available from Amazon: A Treatise on the Modern Law of Real Property and Other Interests in Land .
In the case of an executory limitation which is to take effect in derogation of an estate previously limited by the same instrument, the question whether the failure of such previous limitation to take effect, by reason of the nonexistence of the beneficiary thereof, his death in the testator's lifetime, or for other reasons, will cause a failure of the executory limitation, is a question of the intention, or rather the presumed intention, of the testator or settlor.41 Ordinarily the construction has been adverse to the failure of the executory limitation.42 So in the case of a devise to the child or children of A, but if all such children die under an age named, then to B, the devise over to B has been regarded as taking effect although A has no children, on an inference of intention to that effect.43 And in the case of a devise to A, and if he dies under twenty-one, then over to B, the latter devise was held to take effect when A died under twenty-one in the testator's lifetime.44 But the fact that the prior limitation fails will not ordinarily make the limitation over effective under circumstances which would have excluded such limitation over had the prior limitation taken effect. Thus, in the case of the devise last suggested, if A dies over twenty-one, even though this happens during testator's lifetime, B cannot take, since he was evidently intended to take only in case A died under twenty-one.45 And so it was held that, in the case of a devise to testator's son, and if he dies childless, then over, the devise over did not take effect if the son died in testator's lifetime, leaving a child, although this child also died before testator.46
40. Gore v. Gore, 2 P. Wms. 28; Haywood v. Stillingfleet, 1 Atk. 422.
41. See Mackinnon v. Sewell, 2 Myl. & K. 202. And particularly the editorial notes in 8 Columbia Law Rev. at p. 490, 17 Id. 330.
42. 2 Jarman, Wills, 1642 et seq.; Fearne, Cont. Rem. 237, 509;
Avelyn v. Ward, 1 Ves. Sr. 420; Perkins v. Fisher, 59 Fed. 801; Jossey v. Brown, 119 Ga. 758, 47 S. E. 350; Ege v. Hering, 108 Md. 391, 70 Atl. 221; Burbank v. Whitney, 24 Pick. (Mass.) 146; Mathis v. Hammond, 6 Rich. Eq. (S. C.) 121.