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Journal Article

Female Gametophyte of Microcycas

Lillian Grace Reynolds
Botanical Gazette
Vol. 77, No. 4 (Jun., 1924), pp. 391-403
Stable URL: http://www.jstor.org/stable/2469738
Page Count: 15

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Topics: Gametophytes, Cell nucleus, Ovules, Megaspores, Eggs, Cytoplasm, Canals, Cell walls, Plant cells, Cell growth
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Female Gametophyte of Microcycas
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Abstract

1. The ovules were not young enough to show the megaspore mother cell or the megaspores, the youngest stage of the female gametophyte showing free nuclear condition in the megaspore. 2. In older ovules, nuclear division has increased the number of free nuclei, while at the periphery some of the nuclei are already enclosed by walls. Still older ovules show the gametophyte to be completely cellular. 3. The number of chromosomes is twelve, although occasional nuclei have fourteen. 4. The megaspore membrane increases in thickness from 1.5 μ in August to 3 μ in October, and thereafter decreases to 1.0 μ in March. 5. The cells of the nucellus adjacent to the gametophyte are early organized into a nutritive jacket, which persists until the middle of December. 6. The vascular bundles belonging to the inner fleshy layer of the ovule divide and give rise to branches which enter the nucellus. 7. The archegonial initials are distinguishable about the latter part of November. They are scattered in groups over the surface of the gametophyte, but only those at the micropylar end develop, The remaining initials may divide and become almost unrecognizable among the other gametophyte cells, or may become merely multinucleate. 8. The development of the archegonia is the same as in other cycads, with the exception that in some cases a ventral canal cell is formed. 9. Haustoria from the egg protrude through pores in the egg membrane into the cells of the archegonial jacket which surrounds each archegonium. 10. The archegonial chamber is a shallow depression occurring late in the development of the gametophyte, and is not nearly so highly developed as in the other genera. 11. Microcycas should be regarded as one of the more advanced cycads.

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