The Embryo-Sac of Alisma Plantago

The results of the investigation may be summed up as follows: 1. The development of the embryo-sac of Alisma Plantago represents nothing unusual, the fully matured sac having the usual eight nuclei. 2. During the conjugation of the two polar nuclei, the four centrospheres conjugate by couples, resulting in the formation of two new ones for the definitive nucleus. 3. The endosperm is not abundant and comes entirely from the division of the definitive nucleus, the antipodal cells showing no division or fragmentation. 4. The division of the generative nucleus of the pollen occurs in the pollen grain. 5. Both of the sperm nuclei enter with the pollen tube into the embyro-sac, but only the lower one takes part in the act of fertilization, the other one remaining in the tube. 6. The nucleus of one of the synergidæ is entirely absorbed when in contact with the pollen tube. The other one is later also dissolved, its substance being used probably to nourish the large nucleus of the suspensor cell. 7. The centrospheres of the lower sperm nucleus precede it as it approaches the oosphere. 8. The nucleus of the oosphere becomes bulged out on the side nearest the sperm nucleus, and its centrospheres being situated immediately opposite this bulge, travel slightly toward the approaching male nucleus. 9. All the stages preliminary to the conjugation of the male and female nuclei are favorable to, and indicate a conjugation of their centrospheres, at the time of impregnation of the oosphere. 10. After the first division of the oospore, in the development of the proembryo, the three succeeding divisions take place each time in the outermost cell, the first three divisions being transverse to the long axis of the embryo-sac, the fourth one longitudinal.