The External stem structure and functions

Aimed at RHS level 2 Principles of growth and development studnts

1. External structure of stems

2. Lesson Aims Identify and describe the external features of a stem, including nodes, internodes, buds, and lenticels, and their roles in plant growth and development. Differentiate between specialised stem types, such as stolons and rhizomes, and explain their adaptations and roles in plant propagation and survival. Analyse how external stem characteristics, such as terminal bud scars and leaf scars, can be used to determine plant age, growth patterns, and pruning techniques.

3. Eudicots Woody perennials Monocots

4. https://feralforaging.com/fundamentals-of-winter-tree-identification/

5. A stem has nodes. Leaves and buds (and branchlets) form at the nodes. Nodes

6. The stem region between nodes is called an internode Internode

7. If a plant is growing slowly its internodes are short. If it grows rapidly the internodes will be longer. Each ring around the trunk of this Kentia Palm is a leaf scar or node. It has experienced a period of slow growth then recovered.

8. ‹#› Palms and Tamarix are good wind resistant plants. Wind-resistant plants have flexible stems, which allow them to bend and sway without breaking. Plants that are adapted to windy conditions usually have small, narrow leaves as well, such as needle-leaved conifers and ornamental grasses.

9. Some plants have stems that grow above or under the ground. We know they are stems, not roots, because they have nodes. Stolons : Stem that grows horizontally above the soil surface e.g. Ranunculus repens, Trifolium repens, Fragaria x ananassa Rhizomes : Underground stems that produce roots on the lower surface and extend leaves and flower shoots above ground e.g. Achillea millefolium, Iris sp .

10. ‹#› Left: stems of Elymus repens (couch grass) & Right: Rubus fruticosus (blackberry) are used as colonising agents .

11. S pecialized stems: Stolons and Rhizomes ‹#› Low maintenance Tend to be relatively short lived perennials Partially protected from environmental extremes via linkages and subsurface stems Faster to colonise than bulbs Suitable for wilder planting Formal and informal planting schemes May spread unwanted Vulnerable to subsurface pests

12. The bud at the end of the stem is the terminal or apical bud. The buds further down the stem are axillary or lateral buds

13. Basswood, Sycamore, Oak, Sassafras

14. Terminal buds and axillary buds may be protected by bud scales Bud scales

15. Bitternut Hickory, Willow, Tulip Tree, Buckeye

16. Buds only occur at nodes. The arrangement of buds is the same as the arrangement of leaves. eg. Opposite buds = opposite leaves = opposite branches

17. Revision on leaf arrangement on stems

18. Oak, Willow, Viburnum, Ash

19. On a deciduous tree there will be a leaf scar just below each bud, where the leaf fell off. You may be able to see the sealed vascular tissue. Leaf scar

20. White Ash, Mockernut Hickory, Sweetgum, Silver Maple

21. Lenticels are pores on woody stems. These pores allow oxygen to enter the stem. Oxygen is needed for all living cells to carry out respiration. lenticels

22. Redbud, Black Cherry, Tulip Poplar, Box Elder

23. The terminal bud scar is a ring left on the stem where a terminal bud was during a previous winter. The scar goes right around the stem Terminal bud scar

24. Beech, Sweetgum

25. Current seasons wood is the length of stem produced since the current growing season commenced (usually in spring). Current seasons growth Terminal bud scar

26. One year old wood is the growth from last year. It is located between the first and second terminal bud scar Terminal bud scar One year old wood Terminal bud scar

27. We can count the age of a stem by counting the terminal bud scars. Terminal bud scars (3) 4 years old 1 2 3

28. Forsythia sp Rhododendron sp Syringa sp Cotinus sp Some plants only flower on one year old wood. We prune these immediately after flowering, so that the new growth has one full year to mature.

29. Pruning instructions may refer to the age of the wood Some plants, like Wisteria, flower on wood that is one year old or older. We shorten the younger stems and preserve the older branches. •Cut back one year old wood to within three nodes of the two year old wood. •Keep the flower buds, which are plumper than growth buds.

30. Some plants flower on current seasons growth. We prune them, usually in winter or early spring, to stimulate strong new growth in spring that will bear flowers that summer . Hydrangeas and Hybrid Tea roses flower on current seasons wood.

31. Plants do not grow taller from the base. They produce new primary growth, extension growth, from their buds. (A carving on a tree trunk stays at the same height, it jus t gets wider (secondary growth). Branches also remain in the same position).

32. Lopping, cutting a branch part way along its length, stimulates the growth of epicormic shoots and water shoots. These are more likely than the original branches to break off as they grow heavier. New shoots that grow from epicormic buds are not as securely tied in as branches that have grown from primary growth. Lopping makes a tree dangerous.

33. New stems become firmer as they mature over a season. This influences propagation of plants by cuttings Same stem prepared as a Soft Tip Cutting Soft new growth at the tip of a Dahlia stem. Bottom cut below a node Lower leaves removed Larger leaves cut in half to reduce transpiration

34. Bark may develop Tip growth of Camellia sasanquain late summer Same Same stem prepared as a Semi-Hardwood Cutting Flower bud removed Lower leaves removed Bottom cut below a node

35. In winter the stem has usually developed bark and is woody. We take hardwood cuttings (HWC) from deciduous plants in winter Rosa multiflora-with leaves and without leaves in winter. Sloping cut at the top, just above a node Hardwood cuttings –three from the same length of stem. Horizontal cut, just below a node, at the base

36. These hardwood cuttings of Grape are bundled and planted to callus and develop roots.

37. Buds come in a variety of shapes, sizes and textures and can be a good identifying feature, particularly on deciduous plants in winter Fraxinus‘Raywood’,black buds, opposite or whorled, olive green bark. Pyrus calleryana,buds large, bud scales white and pubescent, alternate arrangement. Naked buds–usually actively growing evergreen plants. Protected buds–buds that develop months before they will grow, eg. Deciduous trees, Camellia flower buds. Bud scales fall off as the bud grows

38. VEGETATIVE BUDS on a Claret Ash FLOWER BUD on a palm MIXED BUDS on an Ornamental Pear Different types of buds vegetative, flower and mixed.

39. Mixed buds open with flowers and new leaves together. Apple with spring flowers and new leaves from the same bud

40. Flower buds produce an inflorescence of flowers. These buds are usually larger than vegetative buds Flower bud Vegetative bud

41. A spur is a short, slow growing branch that bears flower buds or mixed buds and forms fruit. It can be important to recognize the different buds when pruning, especially fruit trees. When formative pruning to create structure knowing your plant helps.

42. A bud already contains a miniature shoot or miniature flowers only a small number of these grow into shoots, the remainder lie dormant to act as points of reserve growth. These buds are kept dormant by a plant hormone called Auxin, which is produced by the terminal bud. If the terminal bud is destroyed by fire, insects, frost, pruning etc. the axillary buds are free to grow. Axillary buds

43. Frequent tip pruning creates bushy plants. It removes the auxin produced by the terminal bud.

44. Stem architecture is strongly influenced by the plant hormone Auxin (IAA). Removing the apical bud causes bushiness. Undamaged stem tips can bend toward light (phototropism). ‹#›

45. A uxin