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AGN 4103/6103 Forage and Pasture Crops
LAB 1 - VEGETATIVE STRUCTURE OF FORAGE CROPS
This lab is intended to introduce you to the vegetative characteristics of the two most important plant families, the grasses and the legumes.
A. Roots
1. Functions of roots
The main functions of roots are as follows:
a. They provide mechanical support for the above ground parts.
b. They absorb water and nutrients from the soil.
c. They translocate water and nutrients to the above ground parts.
d. In many perennial and biennial species, they are also sites for food storage. This food reserve is used to keep the plant alive through the winter, to resume growth in the spring or after cutting or grazing. Examples of species that store
food in their roots are alfalfa (Medicago sativa) and red clover
(Trifolium pratense).
2. Structure of roots systems (Fig. 1)
a. Grasses have a fibrous root system. These roots are adventitious, arising from the lowest nodes of the stems.
b. Legumes have a tap root system. The tap root originates from the primary root (radicle) of the seed, and it may have many branches originating from it. Legumes roots may also have root nodules, which are the sites for nitrogen fixation.
B. Stems
1. Function of Stems.
The main functions of stems are as follows:
a. They support the leaves, flowers and fruits.
b. They translocate water and nutrients through the xylem from the roots to other plant parts, and translocate carbohydrates through the phloem from the leaves to the roots and other sites of growth.
c. Green stems contain chlorophyll and may conduct photosynthesis. However, the amount of photosynthesis taking place in the stem is small relative to the leaves.
d. In many perennial plants they function in food storage. Examples of forage species where food is stored in the stem bases are bahiagrass (Paspalum notatum), orchardgrass (Dactylis glomerata) and tall fescue (Festuca arundinacea). Many other s pecies store food in specialized stem structures such as rhizomes
and stolons.
e. In many perennial species, stems function in vegetative propagation.
2. Structure of stems.
Stems of both grasses and legumes are composed of nodes and internodes. (Figs. 2 and 3). In general, the nodes of a grass stem are more prominent than the nodes of a legume stem. Stem elongation in grasses takes place at the base of the
internodes (intercalary meristems), while in legumes stem elongation
takes place from the top (apical meristem).
Development of new tissues takes place from buds at the nodes (axillary meristems). Buds have the potential to develop into flowers, leaves, roots, or other stems or branches.
3. Specialized stems.
In many species, there are modified stems that function in food storage and vegetative propagation. The modified stems usually arise from the lower nodes of the main stem. The specialized stems that are important in forage species are as follows :
a. Rhizomes (Fig. 4)
Rhizomes are horizontal underground stems that can produce new from their nodes. Examples of plant species that store food and propagate themselves with rhizomes are smooth bromegrass (Bromus inermis), Kentucky bluegrass (Poa pratensis) an d johnsongrass (Sorghum halapense).
b. Stolons (Fig. 5)
Stolons are horizontal aboveground stems that can produce new plants from their nodes. Examples of species that store food and propagate themselves with stolons are white clover (Trifolium repens), and bermudagrass (Cynodon dactylon).
c. Tillers (Fig. 6)
Tillers are secondary stems that arise from nodes at the base of the main stem, and are more or less vertical in position. Most grass species have tillers, although corn (Zea mays) is an exception.
d. Crowns
The crown of a plant is a group of modified stems with very short
internodes which occur very close to the soil surface. It usually
functions as a site for food storage and new growth in perennial species. Most forage grasses, and some forage legumes including alfalfa (Medicago sativa) have a crown.
Other modified stems such as tubers, corns, and bulbs can be important in food storage and vegetative propagation, but are generally not important in forage grasses and legumes.
C. Leaves
1. Function of Leaves.
The main function of leaves is photosynthesis.
2. Structure of Leaves.
Leaves are always attached to the stem at a node in both grasses and legumes.
a. The grass leaf is made up as follows: (Fig. 7)
i. The sheath - this is the lower part of the leaf which is attached to the stem at the node, and usually encircles the stem.
ii. The blade - this is the upper part of the leaf that is flattened, and where most of the photosynthesis takes place.
iii. The collar - this is the hinge-like portion that separates the blade and the sheath. The collar may or may not include auricles, which are clawlike appendages on the edges of the collar, and a lingule, which is a thin, membranous
structure located on the inside of the collar next to the stem.
b. The legume leaf is made up as follows: (Fig. 8)
i. The blade - this is the flattened portion where photosynthesis takes place.
ii. The petiole - this is the stalk that connects the blade to the node. In some cases it may be absent.
iii. The stipules - these are small projections located at the base of petiole where it is attached to the stem. These may or may not be present.
Legumes leaves are either simple or compound. (Figs. 8 and 9)
i. Simple leaves - have a single leaf blade.
ii. Compound leaves - blade is divided up into two or more leaflets. Compound leaves which have all leaflets attached to a single point are said to be palmate (Fig. 10), while compound leaves which do not have all leaflets attached
to a single point are said to be pinnate (Figs. 11, 12, and 13).
 3. Leaf venation
The leaf venation is the pattern of veins in the leaf blade.
a. All grasses have parallel venation. This is a nonbranching pattern in which all the veins are parallel to each other and run the length of the leaf blade.
b. All legumes have netlike venation. This is a many branched pattern of veins.
4. Leaf shape
Leaves come in many different shapes. Some of the more important differences in legumes are shown in Fig. 14.

NOTE: Figures have NOT been scanned and loaded
Reference: This lab was adapted from a handout originally prepared by Dr. David Lugg at New Mexico State University