Stem Adaptations Flashcards
What is the role of stems?
Support leaves, flowers and seed heads in positions that are most advantageous for the plants survival and its ability to compete with other plants and for its reproduction.
What do stems do?
- Put the leaves up into the light.
- Green stems can photosynthesize.
- They can adapt to protect or help plants to climb.
List stem adaptations
- Thorns (Crataegus crus-galli)
- Prickles (Rosa canina)
- Stinging hairs (Urtica dioica)
- Propagation (stolons: Fragaria x ananassa)
- Propagation (Rhizomes: Geranium endressii)
- Store nutrients (CORMS)
- Tendrils (Lathyrus odoratus)
- Petiole (Clematis)
Define an apical meristem
An apical meristem sits at the apex of a shoot and initiates cell growth, allowing the shoot to extend.
What is a dormant bud?
A dormant bud is at the side of a shoot,
typically in a leaf axil, and does not normally grow; however following loss of, or damage to, the apical meristem, it is capable of growing.
What is a twining stem?
stems which circle around enabling the stem to grasp a support, so enabling plants with this adaptation to climb up vertically.
Wisteria sinensis.
What is a stolon?
stems which stretch out horizontally and root when they touch the ground, so propagating the plant. Strawberry, Fragaria × ananassa
What is a corm
swollen underground lower parts of a stem, which enables a plant to store nutrients during a dormant season.
Crocus tommasinianus.
What is a thorn?
sharp outgrowths of a stem which enable a plant to attach its stems to bark or the stems of other plants and so climb; it can also be a defensive mechanism to prevent animal climbing.
Rosa canina.
Why is it often possible to propagate woody plants from stem cuttings but not herbaceous plants?
a. In order to propagate a plant, it must have cambium tissue. Vascular cambium is a secondary meristematic tissue that is only found in woody stems and provides the lateral growth of the stem. Herbaceous perennials do not have lateral growth and therefore, have no vascular cambium. Thus, herbaceous perennials are unable to be propagated with stem cuttings.
b. Fully grown herbaceous perennials do not have any cambium. However, when early in the year, the new shoots of a herbaceous perennial have a tiny amount of cambium in the base of the new shoot. If a cutting is taken at this point, it is possible to propagate.
MODEL:
Most woody plants have lateral cambium in their stems, which is a layer of tissue, where cells replicate and which allows the stem (twig or branch) to gradually thicken.
In many species, this cambium layer can be persuaded to grow roots and develop a new shoot, i.e. to form a new plant – which is what
we are doing when we take cuttings.
In herbaceous plants, the mature stems
does not have any lateral cambium, as it is essentially a flowering stem, which
is growing upwards, and not thickening. Without cambium, there is no hope
of new growth being initiated, and so cuttings are impossible.
Suckers on woody plants are sometimes regarded as a problem, but in other circumstances, they might be a boon. Why the difference of opinion?
a. A sucker is a shoot originating underground from the root or stem of a plant.
b. As a plant sends out multiple shoots and forms numerous new clones it may become an invasive and difficult plant to eradicate from the garden.
c. However, if you are planning a habitat restoration site, it may provide a good dense thicket which would be very advantageous for birds and wildlife.
d. Knowing the site and the future needs of the area will determine whether you wish to plant something that produces numerous suckers. An example of a plant with suckers would be Rhus typhina or Musa paradisaica.
MODEL:
Suckers are analogous to the rhizomes of herbaceous perennials. For the purposes of propagation they are very useful, but in most garden situation a mass of new growth around the base of a tree or shrub is seen as untidy, or
needs controlling, to limit the spread of the plant.
The most common and easiest way of propagating herbaceous perennials is by division.
What is division?
Describe using appropriate terms.
a. Division is the simplest method of propagation where parts of the plant that show totipotency are separated
b. In a bulb, such as an Allium sativa, cutting the bulb in half, with roots, leaves and stems exactly the same will produce a second plant. For plants that have multiple base stems, such as herbaceous perennials, division must include both the roots and the stems. An example would be Rudbeckia fulgida var. deamii
You should mention rhizomes, (eg. Rudbeckia) as the key organ enabling divitson of herbaceous plants , rhizomes show strong totipotency. In other cases root tissue is totipotent allowing division.
MODEL:
Division involves digging up a plant and dividing the underground plant tissue. In some cases this will be root tissue, but in most cases it will be rhizomes, i.e. stems, which we are dividing. Since rhizomes naturally produce new (adventitious) roots and shoots regularly, this is a very easy way to propagate these plants.
What might be the advantages, for environmental improvement, and for biodiversity, in having climbers growing up several storeys on buildings? What kind
of support systems might be needed to enable
climbing plants to grow up tall buildings?
a. Advantages during winter will help to insulate the house from the cold, winds and temperature fluctuations. In the summer, the climbers will protect the house from the extreme temperature of the sun, again providing insulation for the house.
b. IF the climber is deciduous the house can receive sunlight for warmth during the winter and in the summer when the plant is in full growth, provide shelter from the extreme heat.
c. Climbers can also create habitat for birds and pollinators.
d. An issue with climbers on the walls is that some plants must be checked often to make sure they are not growing under the eaves into the roof.
e. Support systems will depend on the climber used but mostly a trellis or vertical wires will do:
e.i. Hedera helix has adventitious roots that will cling to the wall so very little support is needed.
e.ii. Plants with tendrils, which are evolved leaves, will need some sort of trellis attached to the wall in order for the tendrils to cling onto the plant. An example of plants would be Vitis vinifera. Best to use a fan trellis to begin the growth up the wall.
e.iii. Plants with prickles will need the support of wires or a trellis for the plant to grow. The Rosa spp. Has prickles that will help to attach to the trellis, but the plant will need full support in order to climb.
e.iv. Plants such as Wisteria sinensis is a twining plant that twists around poles, gutters or anything to gain height, so once it has secured itself to a structure it will climb.
MODEL:
Climbing plants on buildings provide many of the advantages of trees: shade, evaporative cooling, habitat. They can help mitigate some of the negative impacts of the ‘urban heat island effect’, which will increasingly be a problem with climate change. Growing them on, or adjacent to, buildings can help
moderate temperatures inside the building, provide insulation and reduce solar radiation. They can also be visually exciting. However their weight can be considerable, especially when laden with snow or being buffeted by wind, so they need good supports. For anything higher than two storeys a structural
engineer should be involved. Twining climbers only need vertical cables, but many others need a grid like structure to grasp to enable them to climb.
The use of herbaceous perennials in gardens and in public spaces is increasing. Herbaceous plantings can take many different forms. An important functional use is as ground cover. What might be the most useful aspects of perennial species for effective ground cover? What would you look for when selecting plant species?
Ground cover herbaceous perennials are most effective when they spread rapidly and form a very consistent carpet, without gaps. Those under 40cms are particularly useful, anything taller than this can be blown about by wind
and begin to look untidy. Only a minority of perennials are suitable, notably those with rapidly spreading and frequently branching rhizomes, such as Bergenia spp. or Geranium macrorrhizum. These are also easy and cheap to propagate in the quantities needed.
Where is new tissue grown?
Apical meristem
Does a Herbaceous Perennial have lateral meristem?
NO, only woody has lateral meristem for secondary growth.
What is the core of a tree made of?
Dead xylem. As the tree grows laterally the xylem and phloem spread out and middle dies. Rings of the tree are dead xylem.
What must a plant need to vegetatively propagate?
CAMBIUM.
Cells that allow for growth is the site for potential rooting.
- Pith
- Phloem
- Xylem
- Primary Phloem fibers
- Secondary phloem
- Primary phloem fibers
- Cork
8.Cork cambium
9.Phelloderm - Periderm
- Bark
- Outer bark
- Inner bark
- Phloem ray
- Cortex
- Secondary xylem
- Primary xylem
- Vascular cambium
