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Leaf Types

Leaf Types. Introduction to Agriculture Plant Science Unit. Leaf Types. Most leaves have 2 basic parts, the blade and the petiole Blade: the broad flat portion of the leaf Petiole: the stalk that connects the blade to the stem. Leaf Types.

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Leaf Types

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  1. Leaf Types Introduction to Agriculture Plant Science Unit

  2. Leaf Types • Most leaves have 2 basic parts, the blade and the petiole • Blade: the broad flat portion of the leaf • Petiole: the stalk that connects the blade to the stem

  3. Leaf Types • Deciduous plants: lose their leaves in the fall season • Evergreen plants: lose their leaves throughout the year as the leaves age • The individual leaves age and fall off all year and not just in the autumn • The tree appears green year round

  4. Abscission • Abscission layer: a layer of specialized cells on the petiole where the leaf separates from the stem and falls off • Caused by a substance called auxin • During spring and summer months the leaf is growing and produces its own auxin • In the cooler months the growth slows, and a greater amount of auxin is on the stem than the leaf  causes the leaf to drop off

  5. Sessile Leaves • In some leaves there is no petiole • Sessile leaves: leaf is attached directly to the stem • Usually are annuals, they die each year and come back from seed

  6. Vein Types • Parallel veins: run the length of the leaf and are approximately the same distance apart • Net veins: veins that branch out and form a network • Pinnate: veins branch from a main vein that runs the length of the leaf • Palmately veined: has several main veins originating at the base of the leaf

  7. Leaf Arrangement on Stem • Node: part of the stem from which the leaf sprouts and grows • Internode: space between the node • Simple leaf: if only one leaf is attached at the node • Compound leaf: if 2 or more leaves are attached at a node

  8. Leaf Arrangement • Leaves are arranged in several ways on the stem • 3 most common • Whorled: 3 or more leaves originate from the same node • Alternate: only 1 leaf originates from each node and the leaves are not directly across from one another • Opposite: leaves originate from separate nodes directly across from each other

  9. Leaf Shape • Leaf apexes (tip) • Leaf bases (bottom)

  10. Leaf Margins • Entire: the edge is smooth • Parted: the edge has notches

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