. La botanique pour les étudiants en agriculture. Les plantes. 457 graines mi-juin de la deuxième saison, et bientôt la fécondation suit. En plus de sa simplicité, l'caractéristiques notables de l'homme gametophytc sont que les spermatozoïdes n'ont pas de cils et qu'ils sont menés à l'archégone par le tube pollinique. Les semences. Â L'œuf fécondé à premières formes niveaux de cellules, qui constituent un long filament, appelé un suspenseur, à la fin de laquelle l'embryon se développe profondément ancrée dans les tissus nutritifs du gamétophyte femelle. Quand les vieux l'embryon est encore entouré de beaucoup de tissus gamétophytiques appelé endospe

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. Botany for agricultural students. Plants. SEED 457 middle of June of the second season and fertilization soon follows. In addition to its simplicity the notable features of the male gametophytc are that the sperms have no cilia and that they are conducted to the archegonia by the pollen tube. Seed. â The fertilized egg at first forms tiers of cells, which constitute a long filament, called a suspensor, at the end of which the embryo develops deeply imbedded in the nutritive tissue of the female gametophyte. When mature the embryo is still surrounded by much gametophytic tissue called endosperm. While the embryo or the young sporophyte is developing, the ovule and the entire cone continue to enlarge. The integument is transformed into a seed coat, and when mature the seed sepa- Ir rce. ree Fig. 406. â Diagram of the life cycle of the Pine. Starting with the tree at the left, the two kinds of strobili are shown at a and b, the two kinds of sporophylls and their sporangia at c and d, the two kinds of spores at e and /, the gametophytes at g, the mature seed at h, from the embryo of which a new tree develops. rates from the ovulate scale with a long membraneous wing, which enables the seed to float in the air {Fig. 405.) Pine seeds, although usually smaller, are similar in general structure to the seeds of Cycads. They contain a female gametophyte bearing a young sporophyte and a protective covering composed of the integument and the nucellus, the latter persisting as a membrane about the gametophyte or endosperm. The scales of the ovulate strobilus continue their development until the seeds are mature and remain tightly closed so that the seeds are well protected. «â After the cone is mature, the scales dry. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Martin, John N. (John Nathan), b. 18

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