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notes for pharma studs
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STEMS
The Plant Body: Stems FUNCTION OF STEMS • Stems support leaves,
branches and flowers • Transport water and solutes
between roots and leaves. •
• In some plants, stems have specialized functions…
Stems support a display of leaves and sometimes flowers
Stems orient the leaves toward the light and minimize overlap among the leaves.
Asclepias - milkweed
External Form of A Woody Twig • Apical (Terminal) Bud at
twig tip – Growth makes twig longer. – Actively growing (at least
during the growing season) • Axillary (Lateral) Bud
– Can become branches or flowers in flowering plants
– Dormant
External Form of a Woody Twig • Deciduous trees and
shrubs lose all leaves annually
• After leaves fall, you can more easily see the axillary buds with leaf scars below
Apical Dominance Apical dominance refers to
the suppression of the growth of lateral meristems by hormones produced in the apical meristem.
The growth pattern of pines indicates strong apical dominance.
Bushy plants have weak apical dominance.
If apical meristem is removed, plants may become bushier.
Shoot Apical Meristem
Internal Stem
Anatomy (Woody Dicot)
Monocot Stem – cross section
Dicot Stem Cross Section Helianthus annuus- sun flower
Pith
Ring of vascular bundles
Epidermis
Cortex
Epidermis
Collenchyma
Fibers
Phloem
Vascular Cambium
Xylem
Pith
Early Secondary Growth
Vitis vinifera - grape
The vascular cambium secondary vascular tissue
Three years of Secondary Growth Tilia - basswood
Secondary Xylem
Secondary Phloem
Anatomy of a Woody Stem
Modified Stems
Stolons
• Horizontal above-ground stem
• Reproductive function • Classic example of a
plant that produces stolons is strawberry
Tuber
• Underground stem • The "eyes" of a potato
are the nodes (lateral buds) on a stem
• No leaves, but there is an axillary meristem
Rhizomes
• Rhizomes - horizontal stems that grow below ground produce leaves and adventitious roots
• Examples: ginger, irises, ferns, etc.
Bulb
• Large bud with a small stem, surrounded by fleshy leaves
• Adventitious roots at base
• Examples include onion, tulip, and lily
Corm • Resemble bulbs, but
composed of stem tissue w/ papery leaves
• Food storage organ with adventitious roots at the base
• Examples include crocus and gladiolus.
Tendrils
Grape Tendrils
Stems modified to help plants climb they can grow taller without investing in girth
Thorns • Stems modified for
defense (e.g. citrus)
• Be careful: – spines are modified
leaves – prickles are
extensions of the cortex and epidermis
Roses don’t have thorns
Cladophylls • Photosynthetic stems
– In some species the stem is more important for photosynthesis than leaves
Rosette • Rosette – a stem with very short internodes
(not really specialized, but worth mention)