. Botany for agricultural students . Botany. SEED 457 middle of June of the second season and fertilization soon follows. In addition to its simplicity the notable features of the male gametophyte are that the sperms have no cilia and that they are conducted to the archegonia by the pollen tube. Seed. — 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 endosp
. Botany for agricultural students . Botany. SEED 457 middle of June of the second season and fertilization soon follows. In addition to its simplicity the notable features of the male gametophyte are that the sperms have no cilia and that they are conducted to the archegonia by the pollen tube. Seed. — 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- lY ree. yee Fig. 406. — 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 matvu-e 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. ^05.) 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. 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 Martin, John N. (John Nathan), b. 1875.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
