Morphology of Angiosperms; (Morphology of Spermatophytes. Part II)

Morphology of Angiosperms; (Morphology of Spermatophytes. Part II)

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1903 edition. Excerpt: ...Boveri13 with sea-urchins, in forcing more than one spermnucleus to unite with a single egg-nucleus and producing monstrous larval structures. "The presence of the third nucleus, therefore, with its redundant chromosomes, serves to secure the degeneracy of the resulting tissue." This means, of course, that the endosperm is a degenerate embryo, and that the triple fusion is a true sexual union whose normal result has been interfered with by the presence of a non-sexual nucleus in the combination. It is impossible to solve such a problem by a discussion of the data we possess. The phylogeny of the endosperm must be traced, and the place of the polar fusion and of the triple fusion in its history determined before opinions cease to differ as to its morphological character. In view of such facts as we have, however, we are inclined to hold with Strasburger that the endosperm of Angiosperms is a gametophytic structure, and that the polar fusion and the triple fusion are interpolations in its history that do not change its essential character. The fact that endosperm sometimes forms before fertilization indicates that the triple fusion is not an essential prerequisite; the fact that endosperm forms without the polar fusion points at least to the conclusion that it was once developed without it; the indifference of the male nucleus as to which polar nucleus it fuses with (Lilium, Asclepias) does not show the selective attraction connected with sex-fusion; and the further fact that when an undoubted fertilization occurs, whether of egg, of synergid, or of upper polar nucleus, an embryo is the result, indicates that the presence of the male nucleus in triple fusion is of subsidiary rather than of dominating importance. That the fusing male...show more

Product details

  • Paperback | 124 pages
  • 189 x 246 x 7mm | 236g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236638409
  • 9781236638403