. Plant studies; an elementary botany. Botany. 32S PLANT STUDIES gated, and is usually covered by a delicate flap (indusium) which arises from the epidermis (Fig. 296). Occasionally the sori are extended along the under surface of the mar- gin of the leaf, as in maidenhair fern (Adicmtmn), and the common brake (Pteris), in which case they are protected by the inrolled margin (Fig. 298), which may be called a "false ; It is evident that such leaves are doing two distinct kinds of work—chlorophyll work and spore formation. This is true of most of the ordinary Ferns, but some o
. Plant studies; an elementary botany. Botany. 32S PLANT STUDIES gated, and is usually covered by a delicate flap (indusium) which arises from the epidermis (Fig. 296). Occasionally the sori are extended along the under surface of the mar- gin of the leaf, as in maidenhair fern (Adicmtmn), and the common brake (Pteris), in which case they are protected by the inrolled margin (Fig. 298), which may be called a "false ; It is evident that such leaves are doing two distinct kinds of work—chlorophyll work and spore formation. This is true of most of the ordinary Ferns, but some of them show a tendency to divide the work. Certain leaves, or certain leaf-branches, produce spores and do no chlorophyll work, while others do chloro- phyll work and produce no spores. This differentiation in the leaves or leaf-regions is in- dicated by appropriate names. Those leaves which produce only spores are called sporo- phylls, meaning " spore leaves," while the leaf branches thus set apart are called sporophyll branches. Those leaves which only do chlorophyll work are called foliage leaves ; and such branches are foliage branches. As sporophylls are not called upon for chlorophyll work they often become much modified, being much more compact, and not at all resembling the foliage leaves. Such a differ- entiation may be seen in the ostrich fern and sensitive fern (Onoclea) (Fig. 299), the climbing fern (Lygodium), the royal fern (Osmunda), the moonwort (Botrychium) (Fig. 390), and the adder's tongue (OpMoglossum).. Leaflets of two common ferns : A, the common brake (Pteris); B, maidenhair (Adian- tum) ; both showing sori borne at the margin and protected by the infolded margin, which thus forms a false indusium.—Cald-. 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 Coulter, John Merle
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