Most leaves have one large vein called the midrib that - BIOLOGY - 144
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(narrow strap shaped leaves).  Most leaves have one large vein called the midrib that provide the strength to support the leaf.  Most leaves have a petiole (stalk) that holds the leaf blade (also called a lamina ) away from the stem so that it gets more sunlight and isn’t shaded by leaves above it. o In deserts or mountaintops, leaves often lack a petiole o Monocots have long strap shaped leaves that petioles aren’t necessary  Leaf blades can be simple or compound. o Simple - one blade o Compound – blade made of several pieces called leaflets , each attached to a rachis (stem). o Palmately compound – all leaves attach to rachis at the same point o Pinnately compound – leaves attached in two rows  Types of modified shoots
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o Bulbs (onions) o Tubers (potatoes) o Rhizomes (ginger, asparagus, bamboo) o Tendrils (grape vines, garden peas, squash) o Stem succulents (cacti) o Leaf succulents (agave, aloe, yucca)  Phyllotaxy (arrangement) of leaves o Alternate - one to each node, spiraled most common o Opposite – 2 to a node on either side o Whorled – 3 ( rarely more) to each node  Almost all large leaves are compound.  Most leaves are attached to the stem, but in monocots, the base of the leaf is wrapped around the stem and extends down the stem for some length before it is actually attached. This portion is called a sheathing leaf base.  Decidious leaves (those that fall off the plant as they die) produce an abscission zone with two layers of cells: o the outer cells die and break
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Jason Hlebakos
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Plants and People - Chapter 3 - Cells, Tissues, and Organs.docx
Mt. San Jacinto College
Plants and People Chapter 3 Cells, Tissues, and Organs All organism contain protoplas
Plants and People - Chapter 3 - Cells, Tissues, and Organs.docx