. A textbook of botany for colleges and universities ... Botany. BKYOPHYTES 95 Sporophyte.—The fertilized egg (fig. 220) produces the sporophyte (called sporogonium in the bryophytes), which when mature is a spherical body, consisting of a wall layer of sterile cells investing a mass of spo- rogenous cells (figs. 221- 226). In producing this body the egg by succes- sive divisions usually first becomes a sphere of eight cells (octants). Then periclinal (parallel with the surface) walls cut ofT an outer layer of cells (amphitkeciiim) that forms the wall of the sporophyte. The group of inner cell
. A textbook of botany for colleges and universities ... Botany. BKYOPHYTES 95 Sporophyte.—The fertilized egg (fig. 220) produces the sporophyte (called sporogonium in the bryophytes), which when mature is a spherical body, consisting of a wall layer of sterile cells investing a mass of spo- rogenous cells (figs. 221- 226). In producing this body the egg by succes- sive divisions usually first becomes a sphere of eight cells (octants). Then periclinal (parallel with the surface) walls cut ofT an outer layer of cells (amphitkeciiim) that forms the wall of the sporophyte. The group of inner cells is the endothecium, which by successive divisions pro- duces a mass of sporog- enous tissue. The cells produced by the last divisions of the sporog- enous tissue are the spore mother cells, each of which produces a tetrad of spores (fig. 226), dur- ing which process the reduction in the number of chromosomes occurs. The mature sporophyte, therefore, is simply a spore case. The venter of the archegonium grows also, forming a special investing struc- ture, the calyptra (fig. 225). Finally the wall layer of the sporophyte and the layers of the calyptra become disorganized, and the spores are free in the archegonial chamber. The spores upon germination produce the gametophyte Figs. 205-211. — Riccia: development of the an- theridium; 205, first division of the superficial initial cell, the protruding cell to give rise to the antheridium; 206, first transverse division of the antheridial cell; 207, further transverse divisions; 208, the beginning of vertical walls; 209, completion of periclinal walls sepa- rating the wall of the antheridium from the spermatog- enous cells; 210, an almost mature antheridium, show- ing the short stalk, the wall, and the mass of cubical spermatogenous cells in conspicuous blocks; 211, a sperm, showing the biciliate bryophytic type (body of sperm black; adjacent light mass is cytoplasm dragged out of the mother cell).. Please note that thes
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
