Male Cells in Angiosperms. I. Spermatogenesis and Fertilization in Asclepias cornuti

Abstract

1. From the beginning of the study of fertilization in angiosperms, the question of the existence of male cells with living cytoplasm has remained in doubt. 2. True male cells exist in Asclepias Cornuti. 3. During the telophase of the division of the generative nucleus, a very delicate cell plate is laid down in the middle portion of the fragmoplast. The latter occupies only the middle portion of the generative cell, whereas its much extended ends consist of granular cytoplasm. 4. The separation of male cells occurs where the cell plate is laid down. 5. Male gametes reach almost maturity while within the pollen grain, and being supplied with tail-like projections suggest in their general aspect bullheads or spermatozoids of some organisms. 6. The male cytoplasm differs considerably in its structure and relation to stains from the cytoplasm of the pollen grain, being therefore well delimited from the latter. 7. Following their formation, male cells remain in the pollen grain, although quite close to one another, but yet not united, contrary to what has been described for some representatives of angiosperms. 8. The tail-like projections of male cells arise from much out-stretched ends of the generative cell. 9. Within the pollen tube male cells sometimes remain close to one another, and sometimes separate a more or less considerable distance, conserving their peculiar structure and relation to stains. 10. The tail-like projections of male cells are conserved while within the pollen tube. 11. Male gametes just after their penetration into the embryo sac maintain in their structure the unchanged cytoplasm. According to Pianeze, the latter stains red, while the cytoplasm of the pollen tube emerged into the embryo sac stains green. 12. Like the other investigators of the sexual process in angiosperms, the writer did not succeed in observing the penetration of male cytoplasm in the egg. 13. The sperm nuclei, from the moment of their formation up to their fusion with the female nuclei, conserve their spherical shape and resting stage. The writer has never observed them to be vermiform, as shown in Frye's fig. 48 (12). 14. The existence of male cells on the one hand in Asclepias and on the other in Vallisneria, as has recently been shown by Wylie (40), makes very probable their occurrence among other angiosperms. 15. In connection with the new data secured during the last decade, the scheme appended to the paper of Nawaschin and of the writer (25), figuring male gametes of seed plants, must be somewhat changed and completed by including male cells among the sperms in angiosperms.