Cyme , “flat-topped” (viburnum) An inflorescence where the branches are opposite. And each flower, in turn, is formed at the tip of a growing axis and further flowers are formed on branches arising below it. The ‘end’ flower opens first.
<ul><li>The epidermis is the cell layer which covers the outer surface of the leaf. </li></ul><ul><li>There are three basic kinds of epidermal cells: </li></ul><ul><li>ordinary epidermal cells </li></ul><ul><li>2. trichomes or hair cells </li></ul><ul><li>3. guard cells </li></ul>
The ordinary epidermal cells may show a variety of shapes depending on the tree species and are often covered with a waxy cuticle which is secreted by the epidermal cells.
A stoma (plural stomata) is a pore or opening in the epidermis. They form the only openings in the epidermis of the leaf and it is through the stomata that gases move into and out of the leaf. Guard cells control the opening and closing.
As water moves into the vacuoles of the guard cells, their content is increased and so is the pressure against the cell walls. The cell walls begin to stretch. The arrangement of the cellulose and the difference in thickness of the wall causes the outer wall to stretch more than the inner. The outer walls thus pulls the inner walls away from each other causing the pore to open.
Factors which cause stomata to open or close 1. Light generally causes stomata to open and darkness to close. Some plants open their stomata at night when they can take advantage of the cooler evening temperatures for gaseous exchange, thus reducing water loss. 2. Wilting or water deficit (and increase in CO2) causes the stomata of a plant to close thus preventing further water loss from the leaves. 3. Increase in temperature causes stomata to open.
Mesophyll <ul><li>Located between the upper and lower epidermis. It is divided into a dense upper layer (palisade mesophyll) and a lower layer that contains lots of air space (spongy mesophyll). Contains chlorplasts , where photosynthesis takes place. </li></ul>
Xylem…tissues that transport water Phloem…tissues that transport ‘food’ Bundle sheath cells make up the plant “veins” that contain X and P
Leaf Parts Apex Margin Base Petiole Secondary vein Primary vein sinuses lobes simple leaves—1 leaf per petiole Lamina or Blade
Leaf Types Simple leaves Compound leaves (4 types) Pinnately compound Trifoliate Palmately compound Bipinnately compound Leaves or leaflets may be unlobed or lobed
One compound leaf with 7 leaflets Pinnately compound
Parts of Compound Leaves Leaflets Rachis Rachilla Petiole Each picture depicts one leaf! Each leaf is subdivided into leaflets. Look for a bud. Buds only occur on twigs where a leaf attaches. No buds occur at the base of leaflets.
Leaf Arrangement (Composition) Alternate One leaf at each node node