. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. 296 SORI vtilgare, Fig. 159, B, s.), where they appear as small circular brown patches situated over the lateral veins of the pinna;. A similar arrangement obtains in the Male Fern {Nephrodium, Fig. 163, B), but here each sorus is protected by a kidnev-shaped outgrowth (indusitim, In.) of the placenta, which withers when the sporangia are mature. In the Maidenhair Fern (Adiantum, Fig. 159, C, s.) and the Wall Rue {Asplcniuin riita miiraria) the soi'i are near the edges of the pinnules, and are covered hy indu
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. 296 SORI vtilgare, Fig. 159, B, s.), where they appear as small circular brown patches situated over the lateral veins of the pinna;. A similar arrangement obtains in the Male Fern {Nephrodium, Fig. 163, B), but here each sorus is protected by a kidnev-shaped outgrowth (indusitim, In.) of the placenta, which withers when the sporangia are mature. In the Maidenhair Fern (Adiantum, Fig. 159, C, s.) and the Wall Rue {Asplcniuin riita miiraria) the soi'i are near the edges of the pinnules, and are covered hy indusia taking the form of little flaps projecting inwards from the margin, whilst in the Bracken (Ptcris, Fig. 163, D), where the sporangia form a continuous fringe all round the margin of the pinnule, the incurved edge of the latter functions as an inclusium. A peculiar tA'pe of sorus is foimd in the Film}' Ferns (Hymcnoph3'llacec'E), which are so-called be- cause of their delicate fronds, consisting of but a single layer of cells. Though mainly encoun- tered in the Tropics, they are represented in Britain by one or two species [ HymcnophvUnm tiiiibn'dgeiisc. Fig. 164) occurring in damp ca^'es and other humid situations in rocky districts. Here the sporangia arise from rod-like placentae (s.) projecting from the leaf-margin, and each sorus is enveloped at its Ijase in a cup-shaped indusium (;'.). In transverse sections through a fertile pinnule of NcpJirodiiDii filix-mas (Fig. 165), the bulging placenta {pi.) on the underside is seen to be supplied Ijy tracheids (/.) from the o\'erlying vascular bundle. The indusium (/.) appears as an \uubrella-shapcd out- growth, one kn'cr of cells thick, arising from the top of the placenta. On the sides of the latter are l)ornc numerous sporangia in \'arious stages of development,. Fig. 163.—Sori of various Ferns. A, Hart's Tongue Fern [ScoJopendriuyn). B, Male Fern (Nephrodium). C, As- plenium. T), Bracken (Pleris). In., Plea
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
