Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Plant physiology wikipedia , lookup
Plant nutrition wikipedia , lookup
Evolutionary history of plants wikipedia , lookup
Plant reproduction wikipedia , lookup
Plant evolutionary developmental biology wikipedia , lookup
Plant morphology wikipedia , lookup
Perovskia atriplicifolia wikipedia , lookup
THE STEM Competencies: To identify the parts and functions of the stem and its classifications Pre Activity: 1. Get a sample of a STEM (by group) 2. Recall the parts of the stem Stem Functions • Stems have the following 4 functions or jobs: – Support – Conduction – Growth – Storage Support • Stems support the plant’s leaves, flowers, and fruits. Conduction • Like roots, stems contain vascular tissue (xylem and phloem). • Xylem conducts water and minerals. • Phloem conducts the sugars created during photosynthesis. Growth • During the growing season, cell division and elongation are occurring in both the apical and lateral meristems of dicots. • This results in plant growth. • The same things are occurring in the intercalary meristems of monocots. Storage • Stems are sometimes modified to store food and (or) water. • Plants that store large amounts of water in their stems or leaves are called succulents. Succulents • Cacti are examples of succulent plants that store water in their stems. • The spines are modified leaves. Tuber • A potato is a special type of underground stem called a tuber. • Tubers store excess carbohydrates manufactured during photosynthesis. • Don’t confuse tubers with tuberous roots. Tuberous roots are root modifications, tubers are modified stems. Stem – part of the plant above the hypocotyls which bears leaves, flowers and fruits. Hypocotyl - attachment of cotyledon and stem. Stemless plants are Acaulescent plants. External Structures: 1. Nodes and Internodes – points on stem from which leaf develop – Nodes section of the stem between two successive nodes – Internodes Leaf Axil Leaf blade Petiole 2. Buds – undeveloped structure of stem. Types: 1. terminal – tip of the stem 2. lateral – side of stem 3. adventitious – at any point of stem Stem Morphology, continued • Bud: a structure on a stem containing a dormant apical meristem. – Buds are usually, but not always, covered by protective scales. – Can be terminal or lateral in position. – Come in 3 basic types: • Vegetative • Flower • Mixed bud scales naked bud of V. carlesii Stem Morphology, continued • Terminal bud scale scars: mark the location of last seasons terminal bud. • Leaf scars: scars marking the location of last seasons leaves. • Vascular bundle scars: found inside leaf scars, these scars mark the location of the vascular bundles that passed from the stem, through the leaf petiole, and into the leaf blade. 3. Lenticels – corky postules found in older stem which allo gaseous exchange. • Not all stems have lenticels. 4. Stomata - - postules found in younger stem for gas exchange 5. Trichomes – epidermal hairs in young stem for protection and water proof. 6. Leaf scar – marks by falling of leaves. 7. Bundle scar – marks by strand of vascular bundles. SECONDARY GROWTH refers to all growth which takes place as a result of cambial activity – increase in diameter. Additional cells: 1. secondary xylem – within cambium rings 2. secondary phloem – outwardly found. Two Regions become Distinct: Bark – tissue outside cambium rings composed of phloem, pericyle, cortex and periderm. Wood – all tissue inside cambium rings. Woody Dicot Stem Cross-Section Ray Stem Anatomy Terminology • Wood: xylem tissue • Springwood: large, thin-walled xylem cells produced in the spring of the year when water is usually in abundant supply. • Summerwood: smaller, thicker-walled xylem cells produced during the summer when water availability is more limited. Stem Anatomy Terminology • Annual Ring: one annual growth ring represents the amount of springwood and summerwood that has occurred in a single growing season. • Trees growing in the tropics, where the temperature is constant and rainfall occurs daily, do not produce annual growth rings. Springwood-Summerwood Cross-sectional view of a 3-year old woody, dicot stem Vascular Cambium Summerwood yr 3 Springwood yr 1 Summerwood yr 1 Springwood yr 2 Summerwood yr 2 Springwood yr 3 Heartwood • Heartwood: As xylem ages it becomes plugged with resins and other waste products. • When this happens the xylem (wood) becomes stained a dark color. • Heartwood is not functional xylem. It no longer conducts water. • It does, however, help strengthen the trunk of a tree. Sapwood • Sapwood: xylem that is actively conducting water. • Lighter in color than heartwood. • Surrounds the heartwood. Heartwood/Sapwood Transport/ Food Conduction (By Products) Starch – chief reserved substances Latex – milky juice – inorganic materials Resins and Gums – contained intercellular passages – turpentine. Oils – eucalyptus, coconut, soy beans Stem Modifications Spurs • Short, slow-growing stems that bear leaves, flowers, or fruit. • Not found on all species. Rhizomes • An underground stem. • Usually grows horizontally. • Capable of producing new shoots and roots. Iris Stolons • Aboveground stems that “run” across the soil surface. • Horizontally growing. • Produce new shoots and roots. Strawberry stolons Corms • Compressed, swollen vertical stem. • Papery covering. • Found underground. • Crocus and Gladiolus are examples. Gladiolus corms Bulbs • Underground. • Two different kinds: Tunicate bulb – Tunicate bulbs have a papery outer covering. An onion is an example. – Scaly bulbs lack a papery outer covering. Lily bulbs are an example. Scaly bulb Photosynthesis – stem – known as cladophyll Absoprtion – absorbing organs – called haustoria. Tendrils for support PROPAGATION Inarching – rooted plants are joined by tying their stem together. Grafting – 2 fleshy cut stem are boundtogether. Base – stock; grafted – scion Cutting – portion of stem and rooted in loose soil. Marcotting – for fruit bearing – girdling of selected bushes with soil and wrapped in cellophane.