. Botany for high schools and colleges. Botany. Fig. 320.—Cross-section of tliestem of wliicli Fig. 319 is tile diagram, taicen above tlie flf til leaf .—After Nageli. tweea the fifth aud sixth leaves of the preceding figure. The bundles are numbered as in Pig. 319. 542.—In a comparatively small number of instances there are fibro-vascular bundles in the stem which have no connec- tion with the leaves. These are known as cauline bundles. 543.—In the Monocotyledons and many herbaceous Dicotyledons, the fibro-vascular bundles are closed—that is, there is no zone of meristem tissue left between t
. Botany for high schools and colleges. Botany. Fig. 320.—Cross-section of tliestem of wliicli Fig. 319 is tile diagram, taicen above tlie flf til leaf .—After Nageli. tweea the fifth aud sixth leaves of the preceding figure. The bundles are numbered as in Pig. 319. 542.—In a comparatively small number of instances there are fibro-vascular bundles in the stem which have no connec- tion with the leaves. These are known as cauline bundles. 543.—In the Monocotyledons and many herbaceous Dicotyledons, the fibro-vascular bundles are closed—that is, there is no zone of meristem tissue left between the xylem and phloem after these have passed over into permanent tissues. There is, as a consequence, a definite period of growth for the bun- dles, and when any bundle has fully formed all its tissues, no further devel- opment can take place in it. This gen- erally results in definitely limiting the growth of the inter- nodes, and in consequence such plants are as a rule short- lived. The perennial woody-stemmed Dicotyledons, and some of the herbaceous annuals, possess bundles which are open—that is, there is left between the xylem and the phloem a zone of meristem tissue which continues to grow long after the other parts of the bundle have passed over into permanent tis- sues. Plants with such bundles may live and continue to grow for an indefinite time. 544.—A cross-section of the stem of a Palm (Pig. 321) shows it to be composed of parenchyma- tous tissue traversed by myriads of fibro-vascular bundles, which descend from the crown of leaves. Each leaf sends down from its broad insertion numerous bundles, which, in a vertical section, are seen first to pass in toward the centre of the stem, and then to curve downward and finally outward. The centre of the stem is thus softer than the peripheral portion, as in the latter the descending. Fig. 321. — Cross-section of the stem of a palm, ec, cortical zone ; Ig, tile softer interior portion of the stem ; lg\ the ha
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
