73 SPORE-BEARING PLANTS first plants to invade the land were spore-bearing plants. The fact, the first evidence of land plants is the presence of spores in Ordovician rocks. In are reproductive structures. Familiar spore-bearing plants include mosses and Spores ferns. 74 LIFE CYCLE OF SPORE-BEARING PLANTS life cycle of spore-bearing plants differs from that of the more familiar seed-bearing The plants. of generations between diploid (double set of chromosomes) and haploid Alternation (single set of chromosomes) is required for fertilization. Water 75 THE FIRST SEEDS appeared during Late Devonian, although it is not known which plant produced them. plants became more abundant during Carboniferous. Seed-bearing seed is significant because it plants from their dependence on moist The environments and allowed them to inhabit dry land, much as the amniotic egg freed animals from their dependence on wet environments. 76 INVASION OF THE LAND BY PLANTS The invasion of the land by plants profoundly altered the landscape. roots slowed erosion. vegetation led to soil formation. Decaying also provided a food source for animals, which invaded the land after the Plants appearance of land plants. Animals could not have survived on land without a food source (plants) in place. 77 EVOLUTION OF WOOD plants evolved wood, they were able to withstand the pull of gravity and grow taller. As Middle Devonian, the first wood appeared in plants of the genus Rhynia. During Rhynia, a Middle Devonian vascular land with woody tissues called xylem. 78 FIGURE 12-87 THE FIRST TREES first trees were present by Late Devonian. The Carboniferous, trees reached 30 m tall or more, with trunks 1 m in diameter. By 79 CARBONIFEROUS COAL are more plant fossils in Carboniferous strata than in any other geologic interval. There gave Carboniferous its name, because of the vast coal deposits which formed from Plants plant remains in lowland swamps. Coal is dominated by the element carbon. represents an enormous biomass of plants because it takes several cubic meters of Coal wood to make one cubic meter of coal. 80
73 SPORE-BEARING PLANTS The first plants to invade the land were spore-bearing plants. In fact, the first evidence of land plants is the presence of spores in Ordovician rocks. Spores are reproductive structures. Familiar spore-bearing plants include mosses and ferns. 74 LIFE CYCLE OF SPORE-BEARING PLANTS The life cycle of spore-bearing plants differs from that of the more familiar seed-bearing plants. Alternation of generations between diploid (double set of chromosomes) and haploid (single set of chromosomes) Water is required for fertilization. 75 THE FIRST SEEDS appeared during Late Devonian, although it is not known which plant produced them. Seed-bearing plants became more abundant during Carboniferous. The seed is significant because it plants from their dependence on moist environments and allowed them to inhabit dry land, much as the amniotic egg freed animals from their dependence on wet environments. 76 INVASION OF THE LAND BY PLANTS The invasion of the land by plants profoundly altered the landscape. roots slowed erosion. Decaying vegetation led to soil formation. Plants also provided a food source for animals, which invaded the land after the appearance of land plants. Animals could not have survived on land without a food source (plants) in place. 77 EVOLUTION OF WOOD As plants evolved wood, they were able to withstand the pull of gravity and grow taller. During Middle Devonian, the first wood appeared in plants of the genus Rhynia. Rhynia, a Middle Devonian vascular land with woody tissues called xylem. 78 FIGURE 12-87 THE FIRST TREES The first trees were present by Late Devonian. By Carboniferous, trees reached 30 m tall or more, with trunks 1 m in diameter. 79 CARBONIFEROUS COAL There are more plant fossils in Carboniferous strata than in any other geologic interval. Plants gave Carboniferous its name, because of the vast coal deposits which formed from plant remains in lowland swamps. Coal is dominated by the element carbon. Coal represents an enormous biomass of plants because it takes several cubic meters of wood to make one cubic meter of coal. 80
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