. Practical botany. Botany. THE PTEEIDOPHYTES 283 261. The fern plant: the gametophyte and sexual reproduc- tion. Upon moist earth, pots in greenhouses, etc., the asexual fern spores germinate. First a stout green cell is produced, and at its base there appears a hair-lilie cell, the first rhizoid (Fig. 234, B and C). The green cell grows rapidly and soon divides to form a row of cells (Fig. 234, D). Thereafter the tip, by means of a special apical cell, expands into a broad, heart-shaped plant (Figs. 284, E, and 235, A). At the margin this plant is one layer of cells in thick- ness, but along
. Practical botany. Botany. THE PTEEIDOPHYTES 283 261. The fern plant: the gametophyte and sexual reproduc- tion. Upon moist earth, pots in greenhouses, etc., the asexual fern spores germinate. First a stout green cell is produced, and at its base there appears a hair-lilie cell, the first rhizoid (Fig. 234, B and C). The green cell grows rapidly and soon divides to form a row of cells (Fig. 234, D). Thereafter the tip, by means of a special apical cell, expands into a broad, heart-shaped plant (Figs. 284, E, and 235, A). At the margin this plant is one layer of cells in thick- ness, but along the midrib quite a cushion of cells is formed. From the under- side and near the base many grow. The presence of chlorophyll, and contact with moist surfaces neces- sary for water supply, aid the gametophyte in manu- facturing its own food. 262. The fern plant: sex- ual reproduction. Antheridia may be developed upon the filamentous green cells be- fore the heart-shaped gametophyte is formed, or upon the older gametophyte they may develop toward the basal region and on the underside (Fig. 235). The antheridium is a globular structure with a single layer of wall cells (Fig. 236, A), and a central cell in which usually thirty-two or sixty-four sperms are formed. In size and number of cells this antheridium is much simpler than that seen in bryophytes. The sperm is, how- ever, quite complex and seems well constructed for swimming (Fig. 236, By Also on the underside of the gametophyte and nearer the apical region are the archegonia (Fig. 235). Only the necks extend out from the surface, and these usually turn backward. Fig. 235. A, a diagram of the underside of a fully formed fern gametophyte, showing rhizoids, antheridia, and ar- chegonia ; B, a fern gametophyte from which a young sporophyte is growing Both somewhat enlarged. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appeara
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