. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. 72 ACEOGENOUS OR ACOTYLEDONOUS STEM. tion of the walls of the cells in the centre. The bases of the leaves remain long attached, but ultimately fall off, leaving marked scars •which are at first close together, but often separate afterwards by- interstitial growth. On these scars or cicatrices [cicatrix, a wound) the markings of the vessels are easily seen, arranged in the same manner as those of the stem, with which they are continuous. The vascular system of ferns co
. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. 72 ACEOGENOUS OR ACOTYLEDONOUS STEM. tion of the walls of the cells in the centre. The bases of the leaves remain long attached, but ultimately fall off, leaving marked scars •which are at first close together, but often separate afterwards by- interstitial growth. On these scars or cicatrices [cicatrix, a wound) the markings of the vessels are easily seen, arranged in the same manner as those of the stem, with which they are continuous. The vascular system of ferns consists chiefly of scalariform vessels (fig. 64), mixed with annular (fig. 62), woody and pitted vessels (fig. 116 ter). There are no true tracheae with fibres which can be unrolled. In the stems of Lycopodiacese closed tracheae or ducts occur; and in Equi- setaceae the rings of the annular vessels are closely united. The stem of Ferns is generally of small diameter; it does not increase much laterally, after having been once formed, and it does not produce lateral buds. Sometimes it divides into two (fig. 137), by the formation of two buds at its growing point. This, however, is an actual division of the stem itself, and differs from the usual branching of Exogenous and Endogenous stems. In the Ferns of this country the stems usually creep along and under the ground, and the leaves which they produce die annually, with- out giving origin to a conspicuous trunk. In the II % f /I common Brake (Pteris aquilina), the arrange- i I it:"' //' ment of the vascular system may be seen by {*—LS—i/) making a transverse section of the underground ii rn. ^'i stem. The plant has received its name aj-MiKsM, '^' ' from a supposed resemblance to a spread eagle, presented by the vessels when thus cut across. The axis of Lycopodiacese or Club-mosses (fig. 138) exhibits a vascular bundle of scalariform vessels and closed spirals. The bundle is developed in an upward direction as the stem
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
