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PHOTO UNIT 6. THE
FUNDAMENTAL SYSTEM: PARENCHYMA
OBJECTIVES:
1.
Characterize parenchyma in terms of origin, structure, and function
physiologically.
2.
Describe
shape of parenchyma (on the average) and explain the hedral shape
mechanically and analyze deviations from average tetrakaideahedron
organizations.
3.
Elucidate
the importance of intercellular spaces to highly metabolic parenchyma
tissue.
4.
Recognize
ability of parenchyma tissue to become modified in ontogeny in both
structure and function.
Photos for this study:
6-1: Helianthus
(sunflower): t.s. young stem, pith tissue
6-2: A
Helianthus (sunflower):
stem pith ray (dark field)
6-3: Capsella
(shepherd’s purse): t.s. stem pith ray
6-4: Lilium
(lily): t.s. rhizome cortex
6-5
PHOTO STUDY 6-1 Helianthus (sunflower): t.s. young stem, pith tissue
The pith tissue in the center of the stem contains all primary walls. Note a surface view of a wall (all green) with several pores. There are simple pit fields through the primary walls. PHOTO STUDY 6-2 Helianthus (sunflower): stem pith ray
This photo is taken through a pith ray (between bundles of vascular tissue). These cells have secondary walls deposited on the inner surface of primary walls.
PHOTO STUDY 6-3 Helianthus (sunflower): stem pith ray (dark field)
In face-view of a cell wall, note the numerous pore-like pits. These are interruptions in the secondary wall; they do not extend through the primary wall. These pits are simple ones, in the sense that they lack borders. Bordered pits will be seen later in another kind of tissue. Why are pits not evident in sectioned walls…or are they?
PHOTO STUDY 6-4 Capsella (shepherd’s purse): t.s. stem pith ray
Study cells of a pith ray here. Note the greatly thickened secondary wall, its laminated character and its lignification. Here parenchyma tissue has actually become hard and woody; it is practically sclerenchyma tissue now. Identify a simple pit pair in the secondary walls (center), and note that contiguous cells have their pits directly opposite one another, separated only by the pit-closing membranes.
PHOTO STUDY 6-5 Lilium (lily): rhizome cortex, t.s.
Note the cells in the cortex are crowded with grains of stored starch. Starch is stored in plastids called amyloplasts. Parenchyma tissue that you have seen in Capsella and Helianthus is storage tissue too, though the storage material in these instances was water and possibly a variety of soluble substances.
PHOTO STUDY 6-1 Helianthus (sunflower): t.s. young stem, pith tissue
The pith tissue in the center of the stem contains all primary walls. Note a surface view of a wall (all green) with several pores. There are simple pit fields through the primary walls.
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