Specialized Leaves and Stems

Specialized Leaves and Stems - • Bulbs are underground...

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Specialized Leaves and Stems Although typical shoots are erect with photosynthetic leaves, over evolutionary time a great  assortment of modifications of the basic body plan have arisen. Some clearly benefit storage of  materials, others assist in  vegetative reproduction  (reproduction without seeds), various alterations  deter herbivores, and many are simply innovations in ways to hold the shoot upright. The most  bizarre of all may be the leaves of the  insectivorous  plants that are modified to ensnare and digest  hapless insects and other small organisms. Some drown their victims in vase-like rainwater-filled  petioles while others glue them to the leaf with sticky digestive enzymes. The Venus' flytrap, on the  other hand, snaps its leaves together rapidly enough to enclose the unlucky insect that alights on the  trigger hair.  You can see many of the modifications in common garden and edible plants. For example: 
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Unformatted text preview: • Bulbs are underground buds with the stem reduced to a small knob on which fleshy storage leaves are clustered (e.g. dry onions). • Tubers are fleshy underground stems modified to store starch (e.g. white, or Irish, potatoes). The “eyes” are the nodes with an axillary bud in each (the peel is periderm tissue). Sweet potatoes are roots . • Rhizomes are horizontal underground stems with nodes, internodes, dry scale leaves, and adventitious roots (e.g. fresh ginger “roots” sold in grocery stores are rhizomes). Canna lilies, iris, and many grasses have rhizomes with which they are propagated. • Corms are upright underground fleshy stems covered by leaves reduced to dry, covering scales (e.g. gladiolus and crocus). Note that corms store reserve food in stem tissue, and bulbs in leaf tissue....
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