Elementary Botany with Students' Guide to the Examination and Description of Plants

Elementary Botany with Students' Guide to the Examination and Description of Plants

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1883 edition. Excerpt: ...facts. 1. Its first appearance. It arises as a swelling on the placenta; like asmall bud or wart consisting of a mass of cells; or like a lobe growing on the margin of a leaf. This wart-like Vegiigiigiif Aov;l()(le1SIlgoefl. shall call it nucellus, and we gmwing 0" ')' FR' fimme. may compare it with the macrosporangium of the Selaginella. 2. Next an inner wall grows up from the base, then a second wall. This double coat encloses the nucellus, leaving a small entrance (micropyle) at the summit (Fig. 124). We shall call the coats exotest and endotest, and if in ripe seeds a third layer appears between them we shall call it mesotcst. These terms are introduced to avoid ambiguity in the use of the current terminology. 3. One of the cells of the nucellus enlarges, and its lower part forms a chamber, ere long opening to the outer world by the micropyle (Fig. 29, p. 56). In this chamber the embryo is to be produced along with some of its accessories. Hence the chamber is known as the embryo-sac. It corresponds with the macrospore of Selaginella. 4. The nucleus of the embryo-sac divides and subdi A, section of ovule of Pansy (Viola tricolor). pl, placenta, with raphe; a and i, outer and inner coats; p, pollen-tube entering the micro yle: e, embryo-sac; xx, the nucellus; B and c, the young embryo fixe by its proembryo cells within the embryo-sac. Their terminal cells become the true embryo. vides into eight nuclei, four of which occupy each end of the embryo-sac. From each set of four a nucleus travels towards the centre of the sac, and these two "polar-nuclei" meet and coalesce, so as to form the definite nucleus of the embryo-sac. There remain two sets of three nuclei, one at each end of the sac: those at the...show more

Product details

  • Paperback | 86 pages
  • 189 x 246 x 5mm | 168g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236835298
  • 9781236835291