2101 - Stems Flashcards
What is a Stem?
Plant organ which connects the roots of a plant to its leaves and flowers.
Distinguished externally from roots by the presence of leaves and buds from their axils.
Functions of a Stem
Holding leaves in optimum position for Photosynthesis and adequate air.
Transport of Water and Minerals from roots to the leaves.
Transport of Sugars from the leaves to other parts of the plant.
Holding flowers in optimum position for pollination by wind, insect or other vector.
Storage of starch… Solanum tuberosum (potato)
External features of a Stem
Apical Bud (terminal bud) Axillary Buds Nodes Internodes Lenticels Terminal bud scale scars Leaf scars
Shoot
Term for Stem and leaves together.
External features of a Stem - Apical Bud
Contains the shoot apical meristem, surrounded by developing leaves.
Secretes auxins which suppress growth of axillary buds and creates Apical Dominance.
External features of a Stem - Axillary Bud
An undeveloped shoot (a bud) which develops in the leaf axil.
Remains suppressed until Apical dominance is removed and it can grow a new stem.
External features of a Stem - Node
The point of attachment of a leaf to a stem.
External features of a Stem - Internode
The section between nodes on the stem.
Development determined by environmental constraints.
(between nodes only not bud scars and nodes)
External features of a Stem - Leaf Scar
Where leaf petiole has detached from the stem. Corky layer.
Axillary buds found directly above the leaf scar.
External features of a Stem - Terminal Bud Scale Scar
Indicator of the start/end of a season’s growth.
External features of a Stem - Lenticel
Pore in the stem of woody plants.
Allow gaseous exchange between tissues beneath the stem surface and the atmosphere.
(hole through the epidermis)
Internal features of a Stem
Epidermis Cortex Cambium Phloem Xylem Pith Vascular Bundle
Internal features of a Stem - Epidermis
Single Cell layer. Covered with waxy cuticle made of Cutin to protect young stem from waterloss, pest and disease.
Replaced by corky bark (produced by the cambium) after secondary thickening.
Internal features of a Stem - Cambium
Found between the Xylem and Phloem of some plants.
Meristematic, responsable for lateral growth of stems and secondary thickening.
(Divides to create new Xylem & Ploem)
Internal features of a Stem - Xylem
Responsible for transport of water and minerals through the plants. No end walls, so become continuous hollow tube, strengthened by lignin.
Travels up only. Passive physical process.
(lignified cells = wood)
Internal features of a Stem - Phloem
Transports sugars manufactured during photosynthesis to other areas of the plant.
(Areas in need, or to perhaps storage organs such as bulbs and tubers).
Contains sieve tubes and companion cells.
Up and Down. Active process, expends energy.
Called Translocation.
Internal features of a Stem - Pith
Central tissue in the stem.
Contains Parcenchyma cells.
Is a packing tissue adding body to the stem, it can also have a storage function.
Internal features of a Stem - Cortex
Outer layer between the Epidermis and the ring of Vascular Bundles.
Similarly to the Pith may act as strengthening and or storage tissue. It may also be capable of Photosynthesis.
Monocot Stems
Monocots Vascular Bundles are scattered.
Monocots have no vascular cambium, so are not capable of secondary thickening. Therefore cannot increase number of Vascular Bundles after development.
Some Monocots can expand through Parenchyma division and irregular Lignification. Though this is not the same as True Wood.
Dicot Stems
Dicotyledon stem vascular bundles arranged in rings.
Has Vascular Cambium to create new Xylem and Phloem, therefor can increase in lateral growth and create True Wood or Secondary Thickening.
Stem Adaptions - Twining Stems
Twining their stems around a support.
Climbing/Support for plant and height enables better light, air and pollination availability.
Loincera periclymenum (Honeysuckle) Wisteria sinensis
Stem Adaptions - Tendrils
Tenrils with self adhesive pads Parthenocissus quinquefolia (Virginia Crepper)
Stem Adaptions - Prickles
Can be used for climbing/support and also protection. Growth from the epidermal tissue.
Rosa rugosa
Stem Adaptions - Thorns
Modifcation from the Axilary bud.
Pyracantha coccinea
Crataegus monogyna
Stem Adaptions - Corm
Layers of modified stem for perennation.
Provide food for next seasons growth.
Crocosmia ‘Lucifer’
Stem Adaptions - Rhizome
Ground level modified stem for perennation.
Horizontal stem.
Also for Asexual (vegetative) reproduction.
Short internodes with new shoots from the top axially bud and many roots from the lower axially bud.
Iris germanica (Bearded Iris)
Stem Adaptions - Stem Tuber
Potato.
Solanum tuberosum
Stem Adaptions - Water Storage
Echinocactus grusonii
Stem Vegetative reproduction
Runners - Stolons
Stems with long internodes that produce new plants form the end of the stem
Fragaria spp. (Strawberry)
Climbing (NOT ONLY STEMS)
Twining - Stem Twining petiole - Leaf Prickles - Stem Thorns - Stem Spines - Leaf Tendrils - Stem/Leaf Adventtious Roots - Root
