Download Plant Biology

栓皮栎
Quercus variabilis
栓皮栎
Quercus variabilis
Plant Biology-Lecture 6
Leaves: Structure and Function
Learning objective
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Learn the external forms and parts of leaves
Know the difference among different venation and
between simple and compound leaves
Know the structure and function of a typical leaf
Lean the specialized leaves
Explain why the deciduous leaves turn various
colors in the fall and how such leaves are shed
Know at least the uses of leaves by humans
Introduction
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All leaves originate as primodia（叶原基） in
the buds. In early spring, fewer than 200 cells;
 A typical leaf: petiole（叶柄）, blade（叶
片）, stipules(托叶）；
 Leaves of Deciduous plants: one season; the
leaves of evergreen tree: 2-7 years
毛白杨(Populus tomentosa)
Shape, size, color,Appendage
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Duckweeds（浮萍）:1mm in width
 Palm（塞舌尔棕榈）: 6m long
 Giant water lily（王莲）:2m in diameter; 45kg
 Tubular, feathery, cup shaped, needlelike,
 Smooth or hairy, slippery or sticky, waxy or
glossy, pleasantly fragrant or foul smelling,
edible or poisonous,……
Leaf arrangments and its venation
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Phyllotaxy（叶序）: the arrangement of
leaves on a stem.
 Leaf mosaic(叶镶嵌）：
 Alternate arrangement（互生）:
 opposite arrangment（对生）:
 Whorled arrangement（轮生）:
 Fasciation arrangement(簇生)
叶的排列
叶外形
叶尖和叶基
叶缘
复叶
Poaceaea
毛白杨(Populus tomentosa)
Internal structure of leaves
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Three regions: Epidermis, mesophyll, veins
Epidermis: cutin, wax, glands, appendages,
no chlorophyll except for guard cells;
 Stomata:1000-1.2M/cm2; two guard cells
originate from the same parental cell of the
epidermis
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Simples leaf
 Compound leaf:no buds