Elementary Botany

Elementary Botany

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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. 1882 edition. Excerpt: ...thus formed is known as a pollen-tube (fig. 236). These tubes grow down the loose conducting tissue of the style and enter the ovary. The time necessary for this varies from a few hours to several weeks. In the Crocus it takes from twenty-four to seventy-two hours; in the Arum over five days, and in the Orchids even some months. Just previous to this, or about the same time, a change has been going on in the embryosac of the ovule. Usually one or two cells are produced within the embryo-sac at the end away from the micropyle. These are known as antipodal cells (fig. 237, ), and their function is unknown. Soon after their formation two nuclei are produced at the other end of the embryo-sac, round which the protoplasm becomes aggregated, forming two embryonic or germinal vesicles or cells (fig. 237, k). These vesicles appear to be membraneless before fertilisation, but on the approach of the pollen-tube a cellulose coat is formed round each. The pollen-tube passing into the ovary enters the micropyle of one of the ovules, and, arriving at the apex of the embryo-sac, comes in contact with one of the embryonic vesicles, fertilising it by the passage of the fovilla of the pollen into it by osmosis (figs. 238 and 239). The first change that takes place (after the surrounding of the embryonic vesicle by a cellulose coat) is the division of the vesicle into two (fig. 238,11., k). The cl... upper cell being deve loped into a suspending cord, the suspensor or proembryo (fig. 240, et), at the end of which the Fig. 24o.-Formation of embryo or young plant, Fig. 239.--Fertilisation of Canna. I. Apex of the embryo-sac, e, at the time when the pollen tube? psy has just come into contact with the embryonic vesicle, k. II. Fertilised embryonic vesicle separated...show more

Product details

  • Paperback | 52 pages
  • 189 x 246 x 3mm | 109g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236627865
  • 9781236627865