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Chromatin Behavior in the Development and Maturation of the Egg Nucleus of Zamia umbrosa
George S. Bryan and Richard I. Evans
American Journal of Botany
Vol. 43, No. 9 (Nov., 1956), pp. 640-646
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2438828
Page Count: 7
You can always find the topics here!Topics: Eggs, Chromatin, Globules, Nuclear membrane, Chromosomes, Egg masses, Ova, Canals, Cytoplasm, Reticulum
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The behavior of the chromatin during the development and maturation of the egg nucleus of Zamia has been followed in detail using the Feulgen reaction. The central nucleus possesses diffuse chromatin and, commonly, a conspicuous nucleolus. During preparation for division the nucleolus disappears and the condensed chromosomes become evident. The division spindle is intranuclear, and the chromosomes long and slender. Their number appears to be eight. At late telophase the chromosomes are distributed throughout the young egg nucleus. But thereafter two developments take place simultaneously: (1) a rapid enlargement of the egg nucleus to its ultimate huge size; (2) a slow, continuous contraction of the chromosomes into a microscopic mass, which may occupy various positions in the nucleus. The behavior of the chromatin has not been followed previously in any cycad. Fragmentary evidence from the literature suggests that the behavior of the chromatin in Cycas follows that in Zamia. The necessity of a Feulgen study to resolve the conflicting accounts of chromatin behavior in Pinus is discussed. The maturing egg nucleus of Zamia is of further interest in that there is a remarkable modification of the nuclear membrane into a reticulate pattern of ridges and depressions; and, simultaneously, the growth and extrusion of a large number of globules formed within the membrane. The freed globules are capable of limited growth, are vacuolate, and give a negative Feulgen reaction. Such extrusions have not been previously reported from the large egg nuclei of other cycads nor from those of the conifers, but something apparently similar has been found in the large egg of certain lower animals.
American Journal of Botany © 1956 Botanical Society of America, Inc.