Stem Structure Function in Plants

1. T H E S T E M

2. Competencies:To identify the parts and functions of the stem and its classifications

3. Pre Activity:1. Get a sample of a STEM (by group)2. Recall the parts of the stem

4. Stem Functions • Stems have the following 4 functions or jobs: • Support • Conduction • Growth • Storage

5. Support • Stems support the plant’s leaves, flowers, and fruits.

6. Conduction • Like roots, stems contain vascular tissue (xylem and phloem). • Xylem conducts water and minerals. • Phloem conducts the sugars created during photosynthesis.

7. 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.

8. 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.

9. Succulents • Cacti are examples of succulent plants that store water in their stems. • The spines are modified leaves.

10. 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.

11. 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.

12. External Structures: 1. Nodes and Internodes – points on stem from which leaf develop – Nodes section of the stem between two successive nodes – Internodes

13. Leaf Axil Leaf blade Petiole

14. 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

15. 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

16. bud scales naked bud of V. carlesii

17. 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.

18. 3. Lenticels – corky postules found in older stem which allow gaseous exchange. • Not all stems have lenticels.

20. 4. Stomata - - postules found in younger stem for gas exchange

21. Trichomes – • epidermal hairs in young stem for protection and water proof.

22. 6. Leaf scar – marks by falling of leaves. 7. Bundle scar – marks by strand of vascular bundles.

23. SECONDARY GROWTH • refers to all growth which takes place as a result of cambial activity – increase in diameter. • Additional cells: • secondary xylem – within cambium rings • 2. secondary phloem – outwardly found.

24. Two Regions become Distinct: • Bark – tissue outside cambium rings composed of phloem, pericyle, cortex and periderm. • Wood – all tissue inside cambium rings.

25. Woody Dicot Stem Cross-Section Ray

26. 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.

27. 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.

28. 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

29. 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.

30. Sapwood • Sapwood: xylem that is actively conducting water. • Lighter in color than heartwood. • Surrounds the heartwood.

31. Heartwood/Sapwood

32. 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

33. Stem Modifications

34. Spurs • Short, slow-growing stems that bear leaves, flowers, or fruit. • Not found on all species.

35. Rhizomes • An underground stem. • Usually grows horizontally. • Capable of producing new shoots and roots. Iris

36. Stolons • Aboveground stems that “run” across the soil surface. • Horizontally growing. • Produce new shoots and roots. Strawberry stolons

37. Corms • Compressed, swollen vertical stem. • Papery covering. • Found underground. • Crocus and Gladiolus are examples. Gladiolus corms

38. Bulbs Tunicate bulb • Underground. • Two different kinds: • 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

39. Photosynthesis – stem – known as cladophyll

40. Absoprtion – absorbing organs – called haustoria.

41. Tendrils for support

42. PROPAGATION Inarching – rooted plants are joined by tying their stem together.

43. Grafting – 2 fleshy cut stem are bound-together. Base – stock; grafted – scion

44. Cutting – portion of stem and rooted in loose soil.

45. Marcotting – for fruit bearing – girdling of selected bushes with soil and wrapped in cellophane.