The structure & development of the mosses and ferns (Archegoniatae) . eloped leaves of Azolla are all alike. InA. filiculoides the two lobes are of nearly equal size, the loweror ventral one, which is submersed, somewhat larger, but simplerin structure. The dorsal lobe shows a large cavity near its base(Fig. 204, A), which opens on the inner side by a small the outer side the epidermal cells are produced into shortpapillate hairs, which in some species, A. Caroliniana, aretwo-celled. Stomata of peculiar form (Fig. 204, B) occur on 1 Prantl (i), PI. I. Figs. 2, 3. XII LEPTOSPORANGI
The structure & development of the mosses and ferns (Archegoniatae) . eloped leaves of Azolla are all alike. InA. filiculoides the two lobes are of nearly equal size, the loweror ventral one, which is submersed, somewhat larger, but simplerin structure. The dorsal lobe shows a large cavity near its base(Fig. 204, A), which opens on the inner side by a small the outer side the epidermal cells are produced into shortpapillate hairs, which in some species, A. Caroliniana, aretwo-celled. Stomata of peculiar form (Fig. 204, B) occur on 1 Prantl (i), PI. I. Figs. 2, 3. XII LEPTOSPORANGIA T^ HETEROSPORE^ 393 both outer and inner surfaces. The bulk of the leaf iscomposed of a sort of paHsade parenchyma, and the cavity ispartly encircled by an extremely rudimentary vascular ventral lobe of the leaf is but one cell thick, except in themiddle, where there is a line of lacunar mcsophyll, traversed bya simple vascular bundle. In Salviiiia the leaves are of two kinds. The dorsal onesare undivided, and traversed by a single vascular bundle. The. Fig. 203.—Salvinia natans (L.). A, Horizontal section of the stem apex, X450 ; L, young leaf; B,a young leaf, showing the apical cell (.r), X450 ; C, longitudinal section of a segment of aventral leaf, X430 ; D, section of a dorsal leaf; i, lacunee ; h, hair, X 225 ; E, cross-section of thestem, X 50 ; F, the vascular bundle, X225. mature leaf shows two layers of large air-chambers, separatedonly by a single layer of cells, whose walls are like those of theepidermis. From both upper and lower surfaces, but especiallythe former, numerous hairs develop. The ventral leaves are re-peatedly divided, and each segment grows by a definite apical cell ;the segments are long and root-like, and covered with numerouslong delicate hairs, looking like rhizoids. These submersed 394 MOSSES AND FERNS chap. -* 1^ — — • \ leaves doubtless replace the roots. The leaves in Salvinia arearranged in alternating whorls of three, cor
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Keywords: ., bookcentury1800, bookdecade1890, bookidstructuredev, bookyear1895
