Download 8-28-01

The Grass Plant:
 Grass plants are composed of a complex array of leaves, stems, and roots that
arise from a seed and various vegetative propagules.
Leaves: occur alternately on opposite sides of the shoot
Components of the leaf:
 Leaf sheath: (lower portion of leaf) tightly rolled or folded around the main axis
of the shoot
 Leaf blade: (upper portion of leaf) relatively flat, extends outward at an angle
from the sheath
Older leaves are more visible while younger leaves are enclosed within other leaf sheaths
Components of the leaf used for identification:
 Ligule: located at junction of blade and sheath on inner side of the leaf.
Membranous or hairy structure varying in size or shape.
 Collar: opposite of ligule on the outer side of leaf, light green or whitish band.
Varies in color and size.
 Auricles: Claw-like appendages that may or may not be present
Turfgrass Stems:
The crown: is a highly contracted stem with a succession of nodes separated by very
short internodes
 Node: joint of a stem, the region of attachment of leaves to a stem.
 Crowns are located wherever new shoots develop (embryos, axillary buds and
terminals of rhizomes and stolons
 Crowns also serve as storage organs for carbohydrate reserves
The flowering culm: vertical elongated stem that gives rise to the flowering parts of the
grass plant
Lateral Shoots: (stems) develop axillary buds, function of daily phytocome
WS: long days – stolons, rhizomes
CS: short days – tillers
Lateral stems: Rhizome and stolon are lateral elongated stems that emerge from axillary
buds on the crown Extravaginal Development: (rhizome, stolon) penetrates through leaf
sheath
 Stolons are above the surface
 Rhizomes are below the surface ( they are not roots)
 Determinate rhizome: short and turn upward to form a daughter plant
 Indeterminate rhizome: long and tend to branch at nodes aerial shoots emerge
from axillary buds on the stem
Tillering: process by which new aerial shoots emerge intravaginally) from axillary buds
Intervaginal Development: (tillers) form within the enveloping basal leaf sheaths
 Vertical shoots not lateral
 (Tillers are how young seedlings thicken up)
 Tillers are dependent on parent plant until they develop enough leaves
 Separate but help support the plant in whole
Turfgrass Roots: Two types
 Primary (seminal) develop from the embryo during germination (short lived)
 Adventitous (secondary, nodal) emerge from nodes of the crown lateral stems
(life span may be as long as the shoot they support)
Root growth and decline:
 Cool season grasses have root growth in spring and fall roots decline in summer
months
 Warm season grasses root growth is best in summer months
 Some grasses keep there roots for extended periods( Kentucky blue grass) others
are annual rooting that replace much of there root system( Bermuda and Bent
grass)
Leaf formation:
Because the crown is so close to the gown it is not damage by the constant defoliation
caused by mowing
 The crown forms leaf primordial (Lp) initially start as small protuberances which
eventually develop into fully expanded leaves
 Lp appear just below the apical meristem (undifferentiated tissue with cells
capable of division, growing point were new cells are produced entire growing
point is less than 1 mm( grows stems))
 Lp arise from cell division below the apical meristem
 The leaf tip is formed by rapid cell division at the mid point of each Lp
 Subsequent meristamtic activity is restricted to the basal portion of the Lp,
establishing the intercalary meristem (grows grass blades)
 Upper intercalary meristem grows leaf blades
 Lower intercalary meristem grows leaf sheaths
 Oldest portion of the leaf is at the tip
 Newest is at the base of the sheath
 Each new leaf is slightly higher up on the crown than the preceding one
 New mature leaves produce the most photosynthates
 Senescing: phase consisting maturity to death, takes place from tip downward
The turfgrass seed:
 True seed: consists of seed coat, endosperm and an embryo
 Turf seed: dry fruit called a caryopsis, true seed that is enclosed in adhering
floral parts.
 Caryopsis: contains palea, lemma, pericarp (ovary wall), seed coat, endosperm
and embryo
Floral Parts:
 bracts lemma (outer bract)
 palea (inner bract)
 rachilla short stem like structure at base of palea
 embryo – miniature plant
 endosperm – food supply (starch) for sustaining the plant during germination until
it is able to produce its own food via photosynthesis
Embryo:
 scutellum – (seed leaf/cotyledon) source of enzymes located between endosperm
and main body of the embryo
 Epiblast - remains of the seed cotyledon, may not be present, small flap of tissue
on the side of a grass embryo – opposite the scutellum
 Epicotyle – leaves and growing point
 Coleoptile – (sheath) covers the epicotyle protective sheath
 Coleorhiza – sheath covers primary root (radical)
 Primary root – root present only in the embryo – degenerates- replaced by
adventitious roots.
 Root cap – protects the expanding root tip
Germination
Germination: initiation and activation or growth in a seed
Heterotrophic: plant depends on endosperm for food source (during germination)
1.
2.
3.
4.
Seed must imbibe water
Activation of enzymes
Cell division
Differentiation of cell tissues
Chronological Development:
 Coleorhiza pushes through seed coat
 Root pushes through coleorhiza
 Coleoptile pushes through seed coat to the surface
 True leaves push through a micro pore in the coleoptile
 Chlorophyll is produced in the leaves – photosynthesis
 A little later adventitious roots begin to develop
Autotropic: plant produces its own food from photosynthesis (young seedling)
A few things that can go wrong:
 Endosperm runs out ( old seed?planted too deep)
 Desiccation
 Heavy shade