. Fundamentals of botany. Botany. CALAMITES AND LYCOPODS 387 recognized at once as a new feature in life history. By successive divisions the protoplasm of the spore becomes a multicellular body, the prothallus, with richer cells near the apex. Here a number of archegonia form (Fig. 283), and the enlargement of the prothallus, or gametophyte, causes a splitting apart of the old, thick walls of the megaspore, so that the female gametophyte protrudes (Fig. 284, 9).. Fig. 283.—Selaginella Kraussiana, C, section of mature female gam- etophyte, showing three archegonia, two containing eggs, and one
. Fundamentals of botany. Botany. CALAMITES AND LYCOPODS 387 recognized at once as a new feature in life history. By successive divisions the protoplasm of the spore becomes a multicellular body, the prothallus, with richer cells near the apex. Here a number of archegonia form (Fig. 283), and the enlargement of the prothallus, or gametophyte, causes a splitting apart of the old, thick walls of the megaspore, so that the female gametophyte protrudes (Fig. 284, 9).. Fig. 283.—Selaginella Kraussiana, C, section of mature female gam- etophyte, showing three archegonia, two containing eggs, and one (at the left) an embryo with suspensor (sus.). D-G, Stages in the development the archegonium; H, very young embryo (two-celled stage), after first division of the fertilized egg; /, older embryo {Em), with suspensor {s). (After Campbell.) It bears no chlorophyll, living entirely as a parasite on the parental sporophyte, from whence it derives all the food with which it nourishes the embryo. 348. Fertilization.—As throughout the ferns, calamites, and lycopods, fertilization is accomplished by the swimming of the sperm to the mouth of the archegonium, and down the neck-canal to the ripe egg in the venter. Thus while Selaginella is,, in other respects, a land-plant, it retains the aquatic method of fertilization. External water is absolutely necessary in order that the sperm may reach the egg. 349. The Embryo.—After fertilization the oosperm begins to divide. The cell nearest the neck of the arche-. 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 Gager, C. Stuart (Charles Stuart), 1872-1943. Philadelphia, P. Blakiston's son & co.
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Keywords: ., bookauthorgag, bookcentury1900, bookdecade1910, booksubjectbotany
