Macrosporogenesis and Development of the Embryo Sac of Lilium Henryi

Abstract

1. The egg is removed from the macrospore mother cell of Lilium henryi by four divisions instead of three as has usually been described for members of this genus. 2. The nucleus of the macrospore mother cell and its daughter nuclei pass through the heterotypic and homoeotypic divisions respectively without cell division, so that the embryo sac is 4-nucleate. 3. Three of these nuclei pass to the chalazal end of the embryo sac; all four nuclei divide simultaneously. 4. The spindles of the three chalazal nuclei unite and a single bipolar spindle bearing 36 chromosomes is formed. 5. As a result of the third division the embryo sac is again 4-nucleate, two haploid nuclei being at the micropylar end and two triploid nuclei at the chalazal end. 6. Three of these four nuclei, the two with n chromosomes and one with 3n, pass through typical mitoses; the other chalazal nucleus divides in an abortive manner. 7. The cells of the embryo sac are formed as a result of cell-plate formation across the spindle of this last (fourth) division as well as across the persistent spindles of the preceding division. 8. In the process of fertilization one male gamete nucleus unites with the egg nucleus to form the zygote nucleus (2n) and the other male gamete nucleus unites with the two polar nuclei, one small (n) and one large (3n), to form a 5n primary endosperm nucleus. 9. Sixty chromosomes are present on equatorial plates of dividing endosperm nuclei. 10. An examination of preparations showing embryo-sac development in L. speciosum, L. philadelphicum, L. longiflorum var. eximium (L. harrisii), and L. regale reveals a history similar to that here described for L. henryi. 11. The history of embryo-sac development reported here for five species of Lilium is essentially the same as that described by Bambacioni for other members of the Liliaceae. It is very probably the characteristic lily type.