. Text-book of botany, morphological and physiological. Botany. FILICINEJE. 449 The embryo of Salvinia, as long as it is enclosed in the pro thallium, forms, as we have seen, the segments of its apical cell alternately above and below; but when . the apex of the stem is exposed in consequence of its elongation, a torsion takes place to the extent of about-90°, so that the two rows of alternate segments of the apical cell lie right and left, a peculiarity which has also been observed by Hof- meister in Pteris aquilina. The first leaf is the scutiform leaf mentioned above, which is placed medio-
. Text-book of botany, morphological and physiological. Botany. FILICINEJE. 449 The embryo of Salvinia, as long as it is enclosed in the pro thallium, forms, as we have seen, the segments of its apical cell alternately above and below; but when . the apex of the stem is exposed in consequence of its elongation, a torsion takes place to the extent of about-90°, so that the two rows of alternate segments of the apical cell lie right and left, a peculiarity which has also been observed by Hof- meister in Pteris aquilina. The first leaf is the scutiform leaf mentioned above, which is placed medio-dorsaily; then follow a second and third aerial leaf standing singly, after which the definite verticillate arrangement of the leaves at length commences at the fourth node; each whorl thereafter consists of a submerged leaf springing on the ventral side (right or left), which at once branches, and forms a tuft of long filaments hanging down into the water; while two other leaves have quite flat laminae and spring from the dorsal side, touching'the water only with their under surface (Fig. 319). These three-leaved whorls alternate, and thus form two rows of ventral submerged, and four rows of dorsal aerial leaves. Their succession. FIG. 315 a.—A the vegetative cone of the stem of Salvinia nutans, represented diagrammatically and looked at from above; xx projection of the plane which divides it vertically into a right and left half; the segments are indicated by stronger outlines, their divisions by weaker lines ; the succession of the segments is denoted by the letters F—P; B diagram of the stem with three whorls of leaves, its ventral side indicated by vv; -w the first-formed submerged leaf; Li the aerial leaf formed next; £2 the second aerial leaf of the same whorl formed last of all between the two first (after Pringsheim). in age in the whorl, and the position of the whorls (antidromal among themselves), are indicated in Fig. 315 a. The node of the stem which produces
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
