1. Function
2. External Anatomy
3. Internal Anatomy
4. Specialized Roots
5. Roots and Plant Nutrition

• Roots anchor the plant in the substratum or soil.
• Roots absorb water and dissolved nutrients or solutes (nitrogen, phosphorous, magnesium, boron, etc.) needed for normal growth, development, photosynthesis, and reproduction.
• In some plants, roots have become adapted for specialized functions, which will be discussed at the end of the section on plant roots.

II.  EXTERNAL ANATOMY

1. Root cap
2. Region of cell division
3. Region of elongation
4. Region of differentiation or maturation

• Root cap
  • thimble-shaped mass of parenchyma cells at the tip of each root
  • protects the root from mechanical injury
  • Dictyosomes or Golgi bodies release a mucilaginous lubricant (mucigel)
  • cells lasts less than a week, then these die
  • possibly important in perception of gravity (i.e., geotropism or gravitropism)
  • amyloplasts (also called statoliths) appear to accumulate at the bottom of cells; perhaps the plant has a mechanism for sensing this sedimentation of starch-ladened organelles and interpreting this as the direction down.
• Region of Cell Division
  • Apical meristem - cells divide once or twice per day.
  • The transitional meristems arise from the tips of roots and shoots. These include:
    • the protoderm (which forms the epidermis)
    • the ground meristem (which forms the ground tissue)
    • the procambium (forms the primary phloem and xylem).
• Region of Elongation
  • cells become longer and wider
• Region of Maturation or Differentiation
  • root hairs develop as protuberances from epidermal cells
  • increase the surface area for the absorption of water
  • cuticle exists on root but not on root hairs
• Radicle or primary root, taproot system, fibrous root system, adventitious roots, prop roots, and lateral (branch) roots

III.  INTERNAL ANATOMY

Key for the following diagram:

• A. epidermis (outermost layer of cells forming the initial covering on a root).
• B. cortex (ground tissue that surrounds the vascular cylinder or stele).
• C. endodermis with Casparian strip (regulates the flow of water and dissolved substances).
• D. primary xylem (water-conducting tissue found in the vascular cylinder or stele)
• E. primary phloem (food-conducting tissue found in the vascular cylinder or stele)
• The ring of cells beneath the endodermis would be the pericycle (the origin point for the production of lateral roots)
• The band of tissue between the phloem and xylem are remnants of procambium which could lead to the production of the vascular cambium and secondary growth, especially in a woody dicot root.

• Food storage (Carbohydrates)
  • manioc or cassava => the source of starch for making tapioca pudding
  • sugar beets => sucrose
  • Historical FYI: the original Jack O'Lanterns were carved out of rutabagas, turnips, and white potatoes. Americans introduced the practice of using the pumpkin of this purpose.
• Propagative roots adventitious buds on roots near surface of ground that give rise to aerial stems called suckers that form a new plants (e.g., fruit trees, such as cherries/pears, horseradish, Canada thistles, and aspen.
• Pneumatophores - black mangrow "spongy roots" that facilitate gas exchange between atmosphere and subsurface roots.
• Aerial Roots
  • velamen roots of orchids: a thick epidermis to prevent water loss.
  • prop roots of corn for support
  • adventitious roots of ivies, aid in climbing
• Photosynthetic roots of some orchids e.g., vanilla orchid - same source of nature vanilla flavoring.
• Contractile roots some herbaceous dicots and monocots have the ability to contract roods in order to pull the propagative part of the plant deeper into the soil thereby moving the bulb out of the freeze zone during the winter months.
• Buttrees roots looks like stem but really part of the root system; fortifies stem and aids in support.
• Parasitic roots: a haustorium penetrates the stem of a host plant to secure water and/or food. Examples include witchweed, dodder (nonphotosynthetic) and mistletoe (mostly after water, not food).
• Symbiotic roots
  • mycorrhizae or "fungus roots" where a symbiotic relationship forms between a plant and a fungus. In this partnership the fungus provides protection against some types of pathogens and increase the surface area for the absorption of essential nutrients (e.g. phosphorous) from the soil. The plant in return provides food for the fungus in the form of sugar and amino acids.
  • Legumes (e.g., pea, beans, peanuts) form root nodules. Mutualism between a plant and bacteium which allows for the fixation of atmospheric nitrogen to form that the plant can utilized. The bacterium is reward with food and a place to live

V.  ROOTS AND PLANT NUTRITION

• Plants require large amounts of carbon, hydrogen, and oxygen. Majority arrives to the plant in the form of carbon dioxide and water.
• Other elements are essential for growth include the macronutrients and micronutrients.
• Soil is the source of minerals or nutrients used by plants.

• nitrogen (proteins, nucleotides)
• phosphorous (ATP, nucleic acids)
• potassium (movement of materials across membranes)
• calcium (associated with increasing sensitivity of tissues to different plant hormones)
• magnesium (chlorophyll, assists functioning of certain enzymes).
• sulfur (component of cysteine, an amino acid. sulfide bonding in proteins).

• iron (electron transport system in photosynthesis and respiration)
• boron
• manganese
• zinc
• copper (cytochromes in electron transport systems)
• molybdenum (necessary for normal functioning of nitrate assimilation)
• chlorine

EXCESSIVE NUTRIENTS: Excess nutrients can be toxic to plant.

• For example, sodium/chlorine causes wilting (salt run off from streets that are treated to remove ice).
• Excessive amounts of boron, copper, manganese, aluminum are toxic to plants.
• Plant nutrition is linked to the chemical and physical attributes of the soil the plant is growing in.

• Soil Particles - SAND, SILT, and CLAY - mix some soil in a jar with water, and allow it to settle out overnight. The sand will be on the bottom, the silt will be next, and the clay will be on top. Clay is the final product of weathering and is composed of the smallest particles. Loams contain approximately equal amounts of sand, silt, and clay. Cation exchange from the surface of negatively-charged clay particles to the plant is facilitate by trading a cation for a hydrogen ion. Anions do not attach to clay and are frequently leached from the soil before the plant can obtain them (sulfates and nitrates).
• Humus is the decomposing organic matter in soil. Amount varies along a continuum MINERAL SOILS (1-10% humus) To ORGANIC SOILS (about 30 % humus).
• Air -About 25-50% of the volume of soil is air. The amount of air is higher in sandy soils than in clay soils.
• Water - Soil contains chemically bound (locked to minerals and clay particles - unavailable to plants) and unbound water (available to plants).

1. Function
2. External Anatomy
3. Internal Anatomy
4. Specialized Stems

I.  FUNCTION OF STEMS

• Stems support leaves and branches.
• Stems transport water and solutes between roots and leaves.
• Stems in some plants are photosynthetic (e.g., cacti - leaves are reduced to spines to protect against herbivory and reduce water loss).
• Stems may store necessary materials for life (e.g., water [cactus, miscellaneous succulents]; starch, sugar [sugarcane]).
• In some plants, stems have become adapted for specialized functions, which will be discussed at the end of the section on plant stems.

II.  EXTERNAL ANATOMY

REFER TO FOLLOWING DIAGRAM OF A WOODY DICOT STEM:

FYI: Apical dominance refers to the suppression of growth by hormones produced in the apical meristem.  The Christmas tree pattern of pines indicates strong apical dominance.  Bushy plants have weak apical dominance.  If apical meristem is eaten or destroyed, plants may become bushy.

III.  INTERNAL ANATOMY IN FLOWERING PLANTS

Dicotyledon (two seed leaves) and Monocotyledon (one seed leaf) flowering plants.

Monocots (examples include, grasses, lilies, onions, irises, bamboo, corn, rice, etc.)

• no vascular or cork cambium (secondary growth is rare)
• vascular tissue in bundles (primary phloem, primary xylem, procambium, and sclerenchyma fibers) and distributed randomly through the ground tissue
• ground tissue not divided into pith and cortex
• intercalary meristems at base of nodes allow for elongation of stem (e.g., grass, bamboo) among some monocots

Herbaceous dicots (examples include, alfalfa, tobacco, sunflower, tomato, etc.).

• some secondary growth may or may not develop
• vascular tissue in bundles (primary phloem, primary xylem, procambium, and sclerenchyma fibers) but arranged in a circular pattern when stem is observed in cross section
• ground tissue is divided into pith and cortex

Woody dicots (examples include, oaks, hickory, apple, elm, etc.)

• woody dicot stems start out like that in herbaceous dicots, but these develop secondary growth
• lateral meristems allow the stem to increase in girth or diameter
• lateral meristems: vascular cambium and cork cambium (phellogen)
• Further discussion of secondary growth appears in a later section on secondary growth.

IV.  SPECIALIZED STEMS

• Rhizomes - horizontal stems that grow below the ground with adventitious roots; examples are irises, grasses.
• Stolons or runners - horizontal stem that grows above the ground with long internodes; examples are strawberry, airplane plants.
• Tubers - accumulation of food at the tips of underground stolons, after the tuber matures the stolon dies, the "eyes" of a potato are the nodes of a starch-ladened stem.
• Rosette - stem with short internodes and leaves attached at nodes
• Bulbs - large buds with a small stem at the lower end surrounded by numerous fleshy leaves, adventitious roots at base; examples include onion, tulip, lily.
• Corms - resemble bulbs but composed entirely of stem tissue surrounded by a few papery scale like leaves, food storage organs with adventitious roots at the base of corms; examples include crocus and gladiolus.
• Cladophylls - leaf-like stems; examples include butcher's broom, asparagus.
• Cacti - stout fleshy stems that are modified for food and water storage and photosynthesis.
• Thorns - honey locust (modified stem), black locust and some species of Euphorbia ( spines are stipules), roses (thorn or prickles arise from epidermis).
• Tendrils - for climbing; for example, grape and Boston ivy (English ivy - adventitious roots not stem).

Please refer to the flow charts of primary and secondary growth in stems and roots that were handed out in lab.  Vascular cambium produces secondary phloem and xylem.  The study of woody plant growth over time by examining the annual rings created by secondary xylem is known as Dendrochronology. 

Keep in mind that the periderm arises from the growth and production of cork (dead and suberized at maturity) and parenchyma (lenticels - allows for gas exchange) from the cork cambium .   The periderm replaces the outer covering of the plant as it increases in girth.  The bark includes the periderm and any other tissue (living or dead) from the outermost part of the tree to the cylinder of the vascular cambium in the stem and the root.

1. Function
2. External Anatomy
3. Internal Anatomy
4. Specialized Leaves

I.  FUNCTION OF LEAVES

• Leaves are the solar energy and CO₂ collectors of plants.
• In some plants, leaves have become adapted for specialized functions, which will be discussed at the end of the section on plant leaves.

II. EXTERNAL ANATOMY

• Leaves possess a blade or lamina, an edge called the margin of the leaf, the veins (vascular bundles), a petiole, and two appendages at the base of the petiole called the stipules.
• Arrangement of leaves on a stem = phyllotaxy.
  • whorled - three or more leaves at a node.
  • opposite - two leaves attached at the same node.
  • spiral or alternate - one leaf per node.
• Leaf types (Simple, compound, peltate and perfoliate).
  • Simple leaf = undivided blade with a single axillary bud at the base of its petiole.
  • Compound leaf = blade divided into leaflets, leaflets lack an axillary bud but each compound leaf has a single bud at the base of its petiole.
    • pinnately-compound leaves: leaflets in pairs and attached along a central rachis; examples include ash, walnut, pecan, and rose.
    • palmately-compound leaves: leaflets attached at the same point at the end of the petiole; examples of plants with this leaf type include buckeye, horse chestnut, hemp or marijuana, and shamrock.
  • Peltate leaves = petioles that are attached to the middle of the blade; examples include mayapple.
  • Perfoliate leaves = sessile leaves that surround and are pierced by stems; examples include yellow-wort and thoroughwort.
• Venation = arrangement of veins in a leaf.
  • Netted-venation = one or a few prominent midveins from which smaller minor veins branch into a meshed network; common to dicots and some nonflowering plants.
    • Pinnately-veined leaves = main vein called midrib with secondary veins branching from it (e.g., elm).
    • Palmately-veined leaves = veins radiate out of base of blade (e.g., oak, maple).
  • Parallel venation = characteristics of many monocots (e.g., grasses, cereal grains); veins are parallel to one another.
  • Dichotomous venation = no midrib or large veins; rather individual veins have a tendency to fork evenly from the base of the the blade to the opposite margin, creating a fan-shaped leaf (e.g., Gingko).

III. INTERNAL ANATOMY

• Epidermis = single layer of epidermal cells (containing no chloroplasts) that interlock with one another on the upper (adaxial - toward the leaf axis) and lower (abaxial - away from the leaf axis) side of the leaf blade; the outer surface is often coated with a waxy substance called cutin to form the cuticle (to prevent excessive water loss) and the hair-like structures called trichomes.
• In the epidermis are pores called stomata (pl.), stoma (singular), which allow for gas exchange.  Stomata are formed by two guard cells, which regulate the opening and closing of such pores. In dicots, guard cells tend to be sausage-shaped, whereas in monocots, these tend to be shaped like a bone or a fattened capital letter I.  Guard cells possess chloroplasts. When water is pumped into the guard cells, these tend to bend away from one another creating the opening; when water is pumped out of these cells, the cells become more cylindrical in shape and the stomata close.
• Beneath the upper layer of epidermis, are a rows of vertically-positioned chlorenchyma cells that form the palisade mesophyll. Just below this layer exists bag-like chlorenchyma cells that are loosely packed together which form the spongy mesophyll. The chloroplasts in these two layers of mesophyll are responsible for photosynthesis. Beneath the lower most portion of the mesophyll is the lower epidermis.
• Veins = vascular bundles xylem (water-conducting tissue) oriented towards the upper side of the leaf, containing phloem (food-conducting tissue) oriented towards the lower side of the leaf, sclerenchyma fibers, and parenchyma tissue (which may form a bundle sheath surrounding the vein).
• Collenchyma may be present in the midrib of the leaf or in the petiole just below the epidermis. Collenchyma serves as strengthening tissue to assist leaves in supporting their own weight and to prevent damage due to motion caused by the wind.
• Many plants are deciduous (able to loose their leaves during cold or dry seasons).

IV. SPECIALIZED LEAVES

• Cotyledons: embryonic or "seed" leaves. First leaves produced by a germinating seed, often contain a store of food (obtained from the endosperm) to help the seedling become established.
• Tendrils - blade of leaves or leaflets are reduced in size, allows plant to cling to other objects (e.g., sweet pea and garden peas).
• Shade leaves = thinner, fewer hairs, larger to compensate for less light; often found in plants living in shaded areas.
• Drought-resistant leaves = thick, sunken stomata, often reduced in size
  • In American cacti and African euphorbs, leaves are often reduced such that they serve as spine to discourage herbivory and reduce water loss; stems serve as the primary organ of photosynthesis.
  • In pine trees, the leaves are adapted to living in a dry environment too. Water is locked up as ice during significant portions of the year and therefore not available to the plant; pine leaves possess sunken stomata, thick cuticles, needle-like leaves, and a hypodermis, which is an extra cells just underneath the epidermis.
• Prickles and thorns: epidermal outgrowths on stems and leaves (e.g., holly, rose, and raspberries; Hypodermic trichomes on stinging nettles.
• Storage leaves succulent leaves retain water in large vacuoles.
• Reproductive leaves, (e.g., Kalanchöe plantlets arise on margins of leave.
• Insect-trapping leaves: For example: pitcher plants, sundews venus flytraps, and bladderworts have modified leaves for capturing insects; All these plants live under nutrient-poor conditions and digest insect bodies to obtain nitrogen and other essential nutrients.
• Bracts:  petal-like leaves
• Flower pot leaves:  Structure to catch water and debris for nutrient collection.

• Window Leaves:  plant is buried in soil with transparent part exposed to light.  Being buried reduces loss of war in arid environments - fairy-elephant's feet.   See the following web site at http://www.plantzafrica.com/plantefg/frithiapulchra.htm or view the picture below.

1. Transpiration and movement of water within the plant body
2. Gutation
3. Movement of food within the plant body

I.  Transpiration - evaporation of water from shoot.

Movement of water and minerals in the xylem is a major process. For example, corn plants transpires almost 500 liters of water during its 4 month growing period.

Water moves in tracheids and vessel members. Tracheids pass water laterally through simple and bordered pits. Vessel elements have an greater diameter and are stacked end to end, so water can flow for longer distances (a centimeter to a meter) before having to transverse a pit.

II.  Gutation results from root pressure (solutes moving into xylem cause water to also move into the xylem from surrounding root cells) when transpiration is negligible. Wet soils at night.

Factors Affecting Transpiration

Wind, Internal concentration of carbon dioxide (low concentrations in leaf cause the stomata to open), wind, air temperature, soil, and light intensity. (Light tends to cause stomata to open in the morning and close in the afternoon).

III.  Movement of food within the plant body - transporting organic solutes

Transport occurs in the sieve-tube members of phloem. Very delicate and easily damaged. This fact has limited a lot of work done on phloem, since it releases callose (glucose polymer) and P-protein (proteinaceous slime) which clog up the sieve-tube plates (perforated).

Process is initiated by active transport of sugars from the leaf cells to sieve-tube. SOURCE (leaves in summer and fall, roots in the early spring) AND SINKS (buds in the spring; fruits, seeds, and roots in the summer and fall) AND THE BULK MOVEMENT OF WATER AND SOLUTES.