BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 25 - THE GRASSES
Grasses are the ecologically dominant plants in the temperate zone areas
with rainfall between 10 and 30 inches/year.
Grasses are found in almost all land areas, plus shallow aquatic habitats.
Grasses equal 25% of the world's vegetation.
Grasses include the grains, the single most important food group; major supplier
of calories for human nutrition, also for nutrition of animals for human
Human agriculture produces roughly 600 million tons/yr each of the three
most widely-used grains: wheat, rice, maize (=corn), equals half of all calories
in human nutrition.
Advantage of grain as food: Dry seeds can be stored for years; are a concentrated
Grasses are used extensively as
fodder for livestock.
II. Characteristics of grasses
Systematics: Grasses belong to family
Poaceae (alternative name
Graminae), has 857 genera, 10,500-11,000 species according to
Wielgorskaya (1995). See the
produced by USDA for details. Grasses are monocots (Magnoliophyta,
Leaves are linear, strap-shaped, have parallel veins
Stems may vary:
Upright stem is a culm, supports the leaves and inflorescence; usually surrounded
by leaf sheaths.
Tillers = secondary stems growing from the base of the main stem; very important
for grain production.
Horizontal stems may spread the grass: thin green stolons or runners at the
soil surface, or thicker underground rhizomes. New shoots can grow from nodes
on stolons or rhizomes.
Root system is fibrous, many small roots growing from the crown; the tap
root dies in the first few days after germination of the seed.
= structure containing all the flowers; very different in grasses.
mature inflorescence with seeds is referred to as a seed head.
may be perfect (= bisexual), as in wheat or rice, or imperfect (= unisexual),
as in maize.
Flowers are adapted to wind pollination: small, inconspicuous, many. The
anthers of the three stamens are large (compared to the whole flower), produce
much pollen. The two stigmas are large and feathery, easily catch pollen.
The caryopsis or grain:
The fruit is a caryopsis or grain, has one seed which makes up most of the
fruit; only several thin layers of fruit wall remain.
The grain normally dries until it is only 5-15% water; most plant tissue
is 75-90% water. The dry grain can easily withstand dry conditions over a
hot desert summer, or cold winter.
several parts [see the illustration] that have specific biological functions:
Endosperm is the bulk of the grain. It is composed of large cells, mostly
inactive, filled with starch grains. This is the part that supplies sugar
to the germinating seed for energy and for synthesis of all cell components.
The embryo is the young plant of the new generation, the product of the
developing zygote. This is commercially known as the germ, and is rich in
proteins, vitamins, and oil.
The bran consists of the outer layers of old fruit wall, seed coat, and aleurone
layer. Most layers are fibrous and contain little of nutritious value. However,
the aleurone layer is rich in proteins and vitamins; this layer produces
and secretes the enzymes that digest the stored starch and other stored foods
of the endosperm.
Milling of grain separates the parts. In whole-grain products, only the chaff
has been removed; the product is brown from the presence of the fibrous bran.
Whole-grain products are more nutritious mostly because of the presence of
the germ or embryo. Advantage of white flour or rice: less insect attack,
less rancidity (oxidation of oils) in storage.
Wheat: Triticum spp.: most widely cultivated grain; top producers
US, Ukraine, China. Adapted to cool dry climate, 12-36 in. rain per year.
Origin and evolution: Wild wheats in Near East. Original diploid wheat =
einkorn (Triticum monococcum), hybridized with goat grass
(Aegilops sp.) to make emmer (T. turgidum), with doubled
chromosomes (tetraploid). Durum wheats descended from emmer. Emmer hybridized
with another goat grass to produce hexaploid bread wheat (T. aestivum).
Modern wheats and their uses: Six
Durum or spaghetti wheats, grown in North Dakota, Canada, southern Europe,
India. Used for pasta, noodles.
wheats: high gluten content causes the wet dough to be elastic and sticky.
It will trap bubbles of gas. A leavening agent (baking soda or yeast + sugar)
is added to provide CO2 bubbles, which are trapped, and the dough
rises. Bread wheat flour is the only flour that can make a dough that rises;
the dough of flat breads made with other grains does not rise. Bread wheats
are grown in United States, Russia, Ukraine, China, Australia, Canada.
regions in the United States; US production third, globally, behind China
and India, and ahead of Russia, France and Canada; see
Wheat is a good source of
and fiber and a variety of
Maize or corn: Zea mays. Maize is preferred name, because
corn refers to other grains in Europe.
Types of modern
corn and their uses
Has hard seed coat, high-moisture cells internally.
Heating produces steam, explodes, turns endosperm inside out. Widely
used by Indians because it didn't have to be ground.
Flour corn, soft endosperm, easy to grind, but attacked by insects.
Dent corn, has soft starch in center, hard on outside; soft starch shrinks
more on drying, leaves dent in kernel. All modern field corns are dent corns.
Major uses are for animal feed, corn meal, cornstarch, high fructose corn
corn, endosperm contains sugar instead of starch, harvested and eaten
Hybrid corn: Seed from cross between two inbred (self-pollinated) lines,
each with specific characteristics, but not very productive. Hybrid has hybrid
vigor, more productive. Seed must be purchased every year; because seed from
the hybrid is F2, segregates for many characters. This type of
corn is widely planted and used throughout the world
of corn are many and varied.
Processing of corn is complex because of its multiple uses.
Kernel colors: pigments may be present in the pericarp (fruit wall), aleurone
layer, or endosperm
Origin and evolution: Central Mexico. Selected from, and evolved from, wild
grass teosinte. In native language, teosinte means mother of corn. Widely
planted by numerous groups of
Americans [REQUIRED READING]. Recent report in Science (28 Jun
1996) is that "change from inedible to edible could come from mutations in
just one small stretch of teosinte DNA" supporting the notion that "large
evolutionary leaps" can results from "minor genetic changes".
Characteristics of both:
tassel (inflorescence of male flowers) at end of stem.
ear (inflorescence of female flowers) on lateral branch. Silk protruding
from ear is mass of individual stigmas, each attached to an ovule that will
become a seed.
Characteristics of teosinte:
ear has 6-10 triangular seeds, each surrounded by hard case called cupule.
Several small ears, several tassels at ends of main and side branches.
Spike shatters easily, scatters seed.
Characteristics of maize:
tassel on main stem only.
one to three ears at ends of short lateral branches.
many seeds on ear, in 14 or 16 rows in modern corn; cupule reduced to red
glumes in modern corn, stays on cob.
Nonshattering seed; no dispersal mechanism, modern corn can't survive in
Importance: Rice feeds more people than any other grain; especially Asia.
Rice is the only grain grown entirely for human food, not animal feed.
and evolution; see also
Rice began as a marsh grass in southeast Asia; evidence of
cultivation 7000 years ago. Majority of cultivated rices are paddy rice,
transplanted to flooded fields; upland rice grown on dry land.
Vegetative and cultural characteristics
Extensive air chambers in stem and roots, allows aeration of submerged parts.
Water fern (Azolla spp.) grows in paddies with rice. Fern has pockets
in leaves, filled with cyanobacterium Anabaena which fixes nitrogen
from the air, makes it available to fern. When fern dies and decays, nitrogen
is available to rice; natural fertilizer.
Grain cultivation, harvesting and milling
are drained for harvesting, either by hand or combine.
Brown rice is dehulled
whole grain, has more vitamins and oil than polished white rice. Diet based
on polished rice may result in beriberi, = thiamine deficiency.
Due to hybridization and natural selection, there are now several kinds of
rice which are a threat to cultivate rice
Extensively cultivated and globally consumed, including the
sake (rice beer) or
VI. Other grains
Hordeum vulgare, brewing, animal feed. Fourth most important cultivated
cereale, important in eastern Europe.
sativa, mostly for horse feed.
Sorghum is the
fifth most important cultivated grass.
sorgham or sorgo, and
millets: several genera and species, origin Africa and India, used for
human and animal food.
Saccharum officinarum. A major tropical crop and principal source
Forage grasses: numerous genera and species. Leaves digestible only by ruminant
animals. Examples include
bluegrass (Poa pratensis),
foxtail millet (Setaria italica) which is also found in birdseed,
various of the wild-ryes such as
crested wheatgrass (Agropyrum desertorum), now widely planted
in the West
Rice (Zizania aquatica), a native American grain of increasing
importance, not closely related to plain rice (Oryza sativa).
VI. Alcoholic beverages from grains
A. Beer and ale: beverages made by fermentation
of sugars from malted barley. Beers and ales contain 0% to 12% (commonly
5%) ethanol or grain alcohol, plus aromatic flavor compounds from grain and
hops, the rest is water. Beers and ales are made in 4 stages:
Tour the Tyne Brewery
site for a more complete explanation, photos, and diagrams.
germinationof barley, until just the new root has emerged from the seed,
about 4 days. Malt = germinated barley. Malted barley is then
dried and ground. Malting produces amylases, enzymes that digest starch
2. Mashing = incubation of
malt in warm water for 2-6 hours, during which time the starch in the grain
is digested to glucose. Additional grains (adjuncts), such as rice
or corn, may be added during brewing. At the end of the incubation,
the brew is filtered; this liquid is wort. Wort is immediatley boiled
with hops (female flowers
of hop plant, Humulus lupulus) for flavor, and sent to fermenting
3. Fermentation = growth
of yeast on the wort in the absence of air. The yeast may be a
top-fermenting yeast (Saccharomyces cerevisiae), which floats, and
produces ale; or a bottom-fermenting yeast (Saccharomyces uvarum),
which sinks to the bottom, and produces beer. Fermentation produces ethanol
and carbon dioxiide. Fermentation takes 7-10 days. Product is green
4. Ales are aged for 2-3
weeks, lagers (which include most beers) for 2-3 months, during which time
flavor develops, and dead yeast and undigested proteins settle out. Beers
and ales may then be pasteurized or filtered for sterility and increased
shelf life; so-called
and beers are unsterilized, have superior flavor but short life. Beers and
ales are then bottle, canned, or kegged.
= an alcoholic beverage made by distilling a grain beer.
Scotch and Irish
whiskies are made from barley beers, not the same as commercial beers.
Bourbon, or corn whiskey, is distilled from fermented corn mash (corn
plus water), invented in colonial North America. By distilling, the
beer is boiled to a vapor, and the vapors that boil off at the lowest
temperatures are condensed; this concentrates the alcohol and flavor and
aroma compounds, leaves much of the water to boil at higher temperature.
these notes for section of grasses
reminder about scientific names
All about rice
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Last revised: Aug 1998 - Barnett