. Text-book of botany, morphological and physiological. Botany. FILICINEM. 431 markable, finding its parallel only among the Ophioglossaceae. In old plants of Pteris aquilina the formation of the leaf commences fully two years before its un- folding:—at the commencement of the second year only the leaf-stalk is as yet in existence, about one inch high. Up to this period its growth has been effected by a single apical cell which is divided by oblique walls in alternating directions; it is now carried on by a number of marginal cells which divide. The pinnae are derived from the segments of the
. Text-book of botany, morphological and physiological. Botany. FILICINEM. 431 markable, finding its parallel only among the Ophioglossaceae. In old plants of Pteris aquilina the formation of the leaf commences fully two years before its un- folding:—at the commencement of the second year only the leaf-stalk is as yet in existence, about one inch high. Up to this period its growth has been effected by a single apical cell which is divided by oblique walls in alternating directions; it is now carried on by a number of marginal cells which divide. The pinnae are derived from the segments of the single apical cell; the veins are formed by the repeated divisions of the marginal cells (Sadebeck). In the summer of the second year the lamina arises for the first time at the apex of this rod-like body, and may be found hidden in the form of a minute disc beneath the long hairs. It immediately bends downwards at its apex, and hangs down like an apron from the apex of the stalk (Fig. 301, B} C, I)). Its growth now proceeds underground, so that it does not begin to unfold till the third spring, when it is raised above ground by the elongation of the leaf-stalk. The whole of the leaves of a rosette of Aspidium. FIG. 301.—Pteris aquilina; A the end of a stem st, the apex lying at ss; by its side at b is the rudiment of a leaf, bs the stalk of a leaf in the second year, at k its lamina enveloped by hairs, K a bud at the back of the leaf-stalk, ?w roots ; B a young leaf in the second year, bs its stalk, / its small lamina with the hairs removed; C longitudinal section of a similar leaf, connected with the transverse section of the stem st, bs and I, as in B; D the lamina of a leaf in the second year seen in front, i. e. on the upper side (X about 5); the first segments have begun to be formed; E horizontal longitudinal section of a branching of the stem, ss s's the two apices, a a brown epidermal tissue, b b brown sclerenchyma, gfibro-vascular bundles. (A, B, C natural si2e.)
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
