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Types of Development from the Central Nucleus of Zamia umbrosa
George S. Bryan and Richard I. Evans
American Journal of Botany
Vol. 44, No. 5 (May, 1957), pp. 404-415
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2438509
Page Count: 12
You can always find the topics here!Topics: Canals, Chromatin, Eggs, Cytoplasm, Nuclear membrane, Ova, Cell nucleus, Cell walls, Fertilization, Botany
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Four distinct types of development, for convenience designated A, B, C, D, may be traced from the division of the central nucleus of Zamia umbrosa. Type A is the common type; the others are of relatively rare occurrence. The ventral canal nuclei formed in Types A and B are regularly persistent, enlarge to a limited extent and at the maturity of the archegonia are conspicuous objects in the upper cytoplasm. Types C and D present two methods by which two large potential egg nuclei may be formed in the archegonia. Type D is unique in that the division of the central nucleus is brought about by fission after two chromatin masses have been formed. The chromatin of both ventral canal nucleus and egg nucleus behaves in a manner practically identical during their maturation and development; and the same pattern is followed without modification in the rarer types. Four neck cells are typical in mature archegonia instead of the two that are commonly reported for the cycads.
American Journal of Botany © 1957 Botanical Society of America, Inc.