. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. VASCULAR SYSTEM OF LEAF 11^, leaves [ Holly) which remain on the plant for more than one year. In passing to the finer and finer ramifications of the vascular system a gradual simplification in structure is apparent. The differentiation of the phloem becomes less and less distinct, its place being taken by a more or less uniform tissue of thin-walled elongated cells, whilst at the ultimate terminations of the bundles it often disappears completely. Simi- larly the xylem- vessels gradually give place to re
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. VASCULAR SYSTEM OF LEAF 11^, leaves [ Holly) which remain on the plant for more than one year. In passing to the finer and finer ramifications of the vascular system a gradual simplification in structure is apparent. The differentiation of the phloem becomes less and less distinct, its place being taken by a more or less uniform tissue of thin-walled elongated cells, whilst at the ultimate terminations of the bundles it often disappears completely. Simi- larly the xylem- vessels gradually give place to re- latively short spiral or reticulate tra- cheids (Fig. i8. A, p. 37), the amount of wood-paren- chjnna diminishing till it dies out. Thus the bundle- ends usually consist only of tracheids surrounded by the sin gl e -1 a y ered parenchyma- sheath. In larger leaves [ Sunflower) the midrib often con- tains several bundles, and ex- treme cases are seen in the Docks (Rumex) and the Rhubarb {Rheum rhaponticiim), where quite a large number of strands occur. On the whole the vascular supply is proportional to the size of the leaf, and this is true also of that of the petiole. In small leaves [ Mouse-ear Chickweed, Cerastiimi, Fig. 55) the latter frequently contains but a single vascular strand orientated as in the lamina, whilst in larger ones there are several bundles usually grouped in the form of a C with the 8. Fig. 54.—Diagrams showing the petiolar struc- ture of A, Sea Holly [Eryngiiwi maritinium) ; B, Dog's Mercury {Mercurialis perennis) ; C, Black Bindweed (Polygonum convolvulus) ; D, Bishop's Weed {/Egopodium podagraria). The shaded part of the bundles represents xylem, the unshaded part phloem. Sc, sclerenchj' Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Fritsch, Felix Eugene, 1879-; Sal
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
