. Introduction to botany. Botany. 278 INTEODUCTION TO BOTANY. Fig. 217. The common scouring rush, or horsetail [Equuetum arvense) A, a plant in early spring condition; , rhizome; , spore-bearing branch; c, collection of spo- rophylls (strobilus, or cone); , foliage branch, which later expands as in 5 ; (.', one sporophyll fromthe cone, showing the stalk (st) and several sporangia (sp). D and E, spore with elaters. A and B, one half natural size; C, magnified about 20 times; /' and E, greatly enlarged patches. In still others, as the maidenhair (^Adiantum) and the bracken fern (^Pteris
. Introduction to botany. Botany. 278 INTEODUCTION TO BOTANY. Fig. 217. The common scouring rush, or horsetail [Equuetum arvense) A, a plant in early spring condition; , rhizome; , spore-bearing branch; c, collection of spo- rophylls (strobilus, or cone); , foliage branch, which later expands as in 5 ; (.', one sporophyll fromthe cone, showing the stalk (st) and several sporangia (sp). D and E, spore with elaters. A and B, one half natural size; C, magnified about 20 times; /' and E, greatly enlarged patches. In still others, as the maidenhair (^Adiantum) and the bracken fern (^Pteris aquilina) and other species of Ptcris, the sporangia are cov- ered by the folded leaf margins — the so-called false indusium. In some, as the sensitive fern, or oak fern (fig. 216), the leaf is differentiated iaito a spore- bearing branch and a chloro- phyll branch. In such cases the former is called the sporo- phyll (spore leaf), and the latter the foliage leaf, the chlorophyll bearer. Settmg apart special structures for special pieces of work (divi- sion of labor), as here shown, ordinarily increases the quan- tity and quality of work done. 262. Horsetails, or scouring rushes. The class of pterido- phytes to which these plants belong once constituted a prominent part of the earth's flora as tree-like plants. They are now \ represented by the sin- gle genus PijiiisetuDi. Fossil remains tell in- teresting stories of the ancestors of these plants which lived ages ago when coal was being formed in 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 Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell, Otis William, 1869- joint author. Boston, New York, [etc. ] Ginn and company
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