Slide Set Notes

Teaching Section Slide Program of the Botanical Society of America

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Slide 1. Section through xylem region of a vascular bundle drawn from electron micrographs. The two drawings show parts of the same section that appeared in two successive meshes of the grid. The space between the two drawings indicates the interruption of the view by a grid bar. The numbers accompanied by letters refers to details in the plates bearing the same designations. The large letters above and below indicate continuity of a cell or a cell column. Parenchyma cells at pc. All other cells are tracheary elements in various developmental stages. Scale line, 10 mm.

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Slide 2. The ontogenetic sequence of primary xylem elements shows, from below upward, the following types of secondary wall thickenings: annular, with rings (arrowheads) widely spaced in the much stretched element; annular, and helical combined in a moderately stretched cell; three helices with coils successively closer together (decreasing stretching); continuous pitted wall with pits not discernible but with two perforated end walls in view. Elongated sclerenchyma cells and short parenchyma cell (overlying pitted vessel with helical thickenings illustrate the type of cell used for the ultrastructural study. X200

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Slide 3. Side wall between two differentiating vessel members. The lower of the two cells is the same that appears to the right above in C (see also figure 1). Fibrous material (fb) is present in vesicles connected with the near wall (open arrows). Large arrows indicate the probable limits of the middle lamella, triangles, connections between the microtubules and plasmalemma. X43 200

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Slide 4. Side wall between two differentiating vessel members. In the cell to the right above, no secondary wall deposition has occurred and the microtubules (arrowheads) are unevenly distributed along the primary wall. In the lower, older cell, the microtubules (arrowheads) are concentrated near the young helical thickenings and absent along the primary wall (pw). Many microtubules are sectioned through their connection with the plasmalemma (triangles). The protoplast is somewhat denser in the younger cell. Stars indicate membrane-bound compartments one of which appears as a bleb from the plasmalemma. X43 200

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Slide 5. Side wall between two vessel members with differentiating helical thickenings that appear in sections. The cell to the right is more advanced in development than the one to the left as is indicated by larger amount of secondary wall deposition. Open arrows point to vesicles between plasmalemma and secondary wall. X10 800

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Slide 6. Wall between older (right) and younger (left) vessel members. In the older cell, the secondary wall is marked swl, in the younger sw22. Microtubules (mt) are massed near the secondary wall in the younger cell. Stars indicate membrane-bound vesicles one of which appears as a bleb from the plasmalemma. Body with small vesicles at bv. In the older cell, the primary wall is partly hydrolyzed and some protoplast residue coats the secondary wall. (Compare with Fig. 13 in Charvat and Esau, 1975). Open arrows indicate extent of connection between primary and secondary walls. X21 600

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Slide 7. Vessel member above, parenchyma cell below. The primary wall is partly hydrolyzed in the vessel member. Protoplasmic residue covers the secondary and hydrolyzed primary wall. This vessel member belongs to an earlier, earlier part of the xylem than the one in B. The wide spaces between the sections of the cells indicate that the cell had undergone considerable stretching. X27 000

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Slide 8. In the vessel member to the right the degradation of the primary wall is almost complete and cytoplasmic residue is left in the cell. To the left, the primary wall is partly hydrolyzed between the coils of the helix (see region marked with the star) and a considerable amount of cytoplasmic debris is present in the cell. The intervals between the sections of the secondary wall in the older cell are longer than in the younger cell because the older helix was subjected to a greater amount of stretching (see Fig. 1). Open arrows indicate the connection between the primary and the secondary walls. X21 400.

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Slide 9. Later stage of end wall degradation.

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Slide 10 (4C) LEFT. A rim of secondary wall material has been deposited around the margin of the end wall delimiting the future perforation. The electron lucent condition of the primary wall layers has extended to the rim. It has been accompanied by thickening of the part of the end wall that has to be removed. X6500 RIGHT. The part of the end wall not covered by the rim has been removed. X6500

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Slide 11. End wall at the same stage of development as the one in B. Vesicles occur near the surface of the exposed wall part and some also within the immature rim. Microtubules near the rim at arrowheads. The protoplasts on the two sides of the wall differ in density and organization. Dilated ER cisternae are indicated by stars. X21 600

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Slide 12. Nucleus in a xylem parenchyma cell. At cw, primary cell wall between two parenchyma cells. X800