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Charles J. Chamberlain
Vol. 61, No. 5 (May, 1916), pp. 353-372
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/2469534
Page Count: 24
You can always find the topics here!Topics: Spermatozoa, Eggs, Cytoplasm, Microsporocytes, Plants, Embryos, Leaves, Chromosomes, Cell nucleus, Mitosis
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1. Stangeria is probably monotypic, with S. paradoxa as its single polymorphic species. 2. At fertilization there is a pairing of chromosomes resembling the pairing in the heterotypic mitosis, so that the number during the metaphase of the first division is apparently haploid, although really diploid. 3. There are two free nuclear periods in the embryogeny, the first comprising 9 or 10 simultaneous mitoses and extending throughout the proembryo, and the second with only 2 or 3 mitoses and confined to the lower part of the proembryo. The embryo and suspensor are formed from the second series. 4. There is an evanescent segmentation of the entire egg, as in Dioon. 5. The young embryo is very narrow and its haustorial structures are more conspicuous than in any other cycad yet described. 6. Polarity, which may appear even at the beginning of embryogeny, becomes more and more marked as development proceeds.