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Embryo Sac and Embryo of Pentstemon secundiflorus

Arthur T. Evans
Botanical Gazette
Vol. 67, No. 5 (May, 1919), pp. 427-437
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Page Count: 12
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1. The embryo sac is developed from a single megaspore. Its antipodals disorganize early. The micropylar end becomes bulbous, while the chalazal end becomes long and narrow and is covered by a distinct tapetum. 2. The mature embryo sac is found to be constantly gorged with starch, due to the non-utilization of the nutritive materials which pass into the sac at a time of inactivity just before fertilization. 3. The endosperm nucleus immediately divides and free nuclei migrate into the chalazal end of the sac, where wall formation begins. The proembryo is pushed into this endosperm by an extreme growth of the suspensor. The micropylar end of the sac disintegrates. 4. Two haustoria are formed, the micropylar by the growth of endosperm cells from the chalazal end into the micropylar end, and the chalazal by a growth of endosperm cells from the chalazal end out into the vascular system. The cells of the latter haustorium are binucleate. 5. False polyembryony occurs rather commonly in this species.