Text-book of structural and physiological botany . Fig. 439. — Plnnse of fronds of Ferns with sori ; I. Aspidhun, the sporangiavisible at the margin of the pekate indusium ; II. Aspleniwn : III. Pterisaqzdlina ; IV. the same with the indusium thrown back to show the mode ofattachment of the sporangia; V. Polypodium, indusium wanting ; VI. Hyineno-phylluin or filmy fern ; VII. the same ; the indusium partly removed to show thesporangia (all magnified). often covered by a membranous skin, the indusium [whichis usually an extension of the epidermis] (Fig. 439 i.). In 314 Structural and Physiologi
Text-book of structural and physiological botany . Fig. 439. — Plnnse of fronds of Ferns with sori ; I. Aspidhun, the sporangiavisible at the margin of the pekate indusium ; II. Aspleniwn : III. Pterisaqzdlina ; IV. the same with the indusium thrown back to show the mode ofattachment of the sporangia; V. Polypodium, indusium wanting ; VI. Hyineno-phylluin or filmy fern ; VII. the same ; the indusium partly removed to show thesporangia (all magnified). often covered by a membranous skin, the indusium [whichis usually an extension of the epidermis] (Fig. 439 i.). In 314 Structural and Physiological Botany. most Ferns the sporangia are provided with an elastic ring,the annulus^ running over the apex, which [by its contrac-tion] causes the sporangium to burst [to allow the escape ofthe spores] (Fig. 440 i.); less often it surrounds the sporan-,
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Keywords: ., bookcentury1800, bookdecade1870, bookpublishernewyorkjwileysons
