This section, will deal with the main points of crop plant vegetative anatomy. In this section we will discuss cellular anatomy, root anatomy, stem anatomy, and leaf anatomy as well as discuss the functions of the various structures.

Plant Cells

The first area to be discussed will be that of the structures and functions of various cellular components.

Figure 1

This is a figure of the various components of a plant cell. At this time refer to Page 1 of the study guide. Under No. 1 you will find a list of the structures to be discussed. As we go through, you will want to list the functions of these components.  The intercellular space is the space located between adjacent cells - usually at the corners of these cells. The primary function of this space is to allow for the movement of gases and solutions between adjacent cells. The outer extremity of each cell is its cell wall. The cell wall is a structure that is unique to plant cells in that animals do not possess a cell wall. The cell wall usually consists of three regions or areas. The first is the middle lamella, which is composed of pectic materials that "cements" adjacent cells together. In other words, the middle lamella is located between each of the cells and tends to hold them together. This will be mentioned again shortly. The next area of the cell wall is that of the primary cell wall. It is mainly composed of cellulose fibers and some pectic compounds that have impregnated the fibers from the middle lamella. To the interior of the primary cell wall is the secondary cell wall and is laid down after cell growth has ceased. It again is composed of cellulose type materials and may become lignified. Ligin is a material that impregnates and strengthens the secondary cell wall. The primary function of the cell wall is to give rigidity and support to the plant.

To the interior of the cell wall is the plasmolemma. This is the outer membrane of the cell and functions to contain the cellular contents - among other things. Located within the cell is the plastids. There are two basic types of plastids - the leucoplasts (or colorless plastids) and the chromoplasts (or plastids with color). An example of a leucoplast (or colorless plastid) is the amyloplast. The primary function of the amyloplast is to store starch produced from photosynthesis. An example of a chromoplast (or plastid with color) is the chloroplast. The chloroplasts contain chlorophyll or the green pigment of plants and is the site of photosynthesis. Leaves and other green tissue contain from 20-100 chloroplast per cell, however, this number is somewhat variable from species to species. The chloroplast is composed of an outer membrane enclosing the grana and stoma. The grana is a membrane structure within the chloroplast and is the location of the light reactions in photosynthesis. The stoma is the fluid material in the chloroplast and is the location of the dark reactions of photosynthesis. This structure will be more fully discussed when we cover photosynthesis. Next is the mitochondria. This is the organelle where respiration largely occurs. Respiration is the degradation or burning of foodstuffs or carbohydrates for the production of energy. 'The nucleus is another organelle and contains the nuclear material (or chromosomes). The chromosomes function in reproduction and for the direction of various cellular activities. The vacuole is an area within the cell surrounded by a membrane called the tonoplast - or the inner membrane of the cell. The fluid material of the vacuole usually contains various salts, pigments, starch grains, oil droplets, and other organic substances. Primary function of the vacuole is for the storage of reserve materials and waste products. Next is the cytoplasm or the matrix material of the cell. This is the fluid material located between the plasmolemma and tonoplast membranes. Function here is to contain the many organelles and many cellular reactions occurring within the cytoplasm. Next is the endoplasmic reticulum, which is a membrane that traverses back and forth through the cytoplasm. It primarily functions as the site of many enzymatic reactions as well as the site of ribosome attachment. The middle lamella, as indicated earlier, is a cementing substance that cements adjacent cells together. It contains, among other things, pectic materials. The last cellular structure is the ribosomes. These are small organelles that attach onto the endoplasmic reticulum and function in the formation of proteins. This will be discussed more fully when we cover reproduction. At this time note and label the structures on the diagram under No. 2 in the study guide.

Root Anatomy

The next vegetative area to be discussed will be that of root anatomy. Refer now to No. 3 in the study guide. Roots function in about 4 main areas. First they anchor the plant in the soil. Secondly, they function in the uptake of water and nutrients. The third function of roots is that of translocating water and nutrients from the point of uptake to the base of the stem. And the fourth function of roots is to act in a storage capacity. This storage function is important in root crops such as sugar beets, carrots, and others and is also important in perennials. In perennials these stored carbohydrates are necessary for the plant to put out again during the following growing season. If one is grazing perennials such as many of the forages like alfalfa, clover, and others it is necessary to get the cattle off early enough in the fall such that adequate carbohydrates can be manufactured and stored in the roots before the tops are frozen off. This will insure a source of regrowth materials the following spring to get the plants far enough along such that they can survive on their own photosynthetic activity.

Figure 2

This figure depicts a longitudinal section of a root. Also, refer to No. 4 in the study guide. At the bottom is an area of cells called the root cap. This functions primarily to protect the cells in the next region – the region of cell division - as they are forced through the soil with its abrasive soil particles. The next area - the zone of cell division - is the area where new cells are continually being formed through repeated cell divisions. These cells are thin-walled and easily ruptured by soil particles were it not for the root cap's protection. Next is the zone of cell elongation. Here the cells take up large amounts of water and increase in volume. The increase in cell volume of these cells is primarily responsible for pushing the root through the soil. The next zone is the zone of cell maturation and differentiation. On this figure this zone is labeled the root hair and mature zones. The fully elongated cells in this zone mature and began differentiating into various tissues such as the xylem, phloem, pith, cortex, and others. This zone, the zone of maturation and differentiation begins where the root hairs first become evident. These root hairs are only extensions of the epidermal cells - as may be seen in the inset drawing on the left of the figure. At the top of the slide other tissues may be noted from a cross-sectional view. Also note near the top of the figure that branch roots have formed. These are different from root hairs and will be discussed shortly. At this time answer the question under No. 5 of the study guide.

Figure 3

This is what a typical dicot root looks like in cross-section. Refer to and fill out No. 6 of the study guide as you go through this section. Note the outer layer of cells-called the epidermis. Primary function is for protection. The next layer is that of the cortex usually a large portion of the cross-sectional area of a root. One of the primary functions of the cortex is to store carbohydrates. This is particularly important in root crops and perennials. The next layer is the endodermis. It largely functions to prevent the outward movement of water from the root. The next layer, the pericycle primarily functions as the area or layer of cells where branch roots originate. These branch roots are very instrumental in water and nutrient uptake. Also near the center of the root is the xylem and phloem. The xylem functions to transport water and nutrients while the phloem primarily transports photosynthates. You may want to make a sketch of this figure in your study guide. At this time answer question No. 7 in your study guide.

Root Systems

Root systems are of two primary types. These are the tap roots and the fibrous roots.

Figure 4

This is an example of a tap root system. This type of root is characteristic of dicot or broadleaf plants. Examples would be cotton, soybeans, and sunflowers. The tap root system is characterized by one main root going downward with several lateral branches coming off the tap root. The example in this slide is of dandelion, which is perennial. Cotton and soybeans would be characterized by a smaller tap root and larger branches.

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Figure 5

This is an example of a fibrous root system which is characteristic of monocot plants. Monocot plants are grasses such as wheat, oats, corn, barley, rye, and others. At this time, answer the questions under No. 8 in your study guide.

Moving above ground, the next vegetative structure is that of the stems.

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Figure 6

Refer to No. 9 in the study guide. This figure shows the general morphology of stems. Also refer to the figure under No. 10 of the study guide. The stem is made up of nodes and internodes. The nodes are enlarged areas on the stem and the internode is the stem region between adjacent nodes. Generally buds are located at most nodes as well as at the tip of the stem - this one being called the apical bud while the buds at the nodes are referred to as lateral or axillary buds.

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Figure 7

Also refer to figure No. 11 of the study guide Like the root tip, the stem tip is divided into regions. The tip area is called the zone of cell division, or meristematic zone, and is where new cells are continually being produced through cell division. These are the cells that will constitute the mature plant. Note that no cap, synonymous with the root cap, is present here. Such is not needed for protection as was the case for the root tip. The next area is the zone of cell elongation where the cells rapidly take up water and thus, enlarge. It is in this area that the vascular tissue begins to develop and is referred to as the provascular tissue. The third area is the zone of maturation and differentiation. Here the cells mature and differentiate into various tissues - e.g. xylem, phloem, cambium, etc.

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Figure 8

This is an actual picture of a stem tip. Can you identify the various regions and structures? At this time answer the questions under Nos. 12 and 13 of your study guide.

Refer to No. 14 of your study guide. The next topic to be discussed is that of modified stem structures.

Figure 9

The first modified stem structure to be discussed is that of a corm. A corm may be defined as the enlarged base of a stem, which is short, fleshy, and has few nodes and few leaves. Gladiolas and Timothy are two examples of plants that have corms. By noting the figure it may be observed that the corm is indeed the enlarged base of the stem. Originating from the lower portion of the corm is the developing adventitious roots. On the corm itself the nodes may be discerned as well as developing lateral buds and also newly developing corms. Coming out of the top of the corm is a new flower stem, which may give rise to a new plant. It should also be noted that the lateral buds are developing at the nodes as was the case on regular stems.

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Figure 10

The second type of stem modification is that of the rhizome. A rhizome may be defined as a horizontal underground stem, which has nodes and internodes. In addition, leaf scales and buds may also be evident.

Examples of two species having rhizometous growth would be bermudagrass and johnsongrass. The rhizomes are very important in terms of vegetative reproduction in that the rhizomes spread beneath the soil surface and at the nodes new shoots may originate giving rise then to new plants complete with roots, stems, leaves, and seed heads. In plants like bermudagrass this is very desirable in that this type of vegetative reproduction is important in spreading of the plants to fill in the soil surface area. However, for undesirable species - for example Johnsongrass - this type of vegetative reproduction is very undesirable in that it leads to the proliferation of this undesirable species.

Figure 11

This figure shows an actual photograph of the basal part of a stem with its included rhizomes. The area labeled No. 1 on this slide depicts a newly developing rhizome and that labeled 2 is the main part of the stem from which the new rhizome is originating.

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Figure 12

The third type of stem modification is that of the stolon. The stolon may be defined as a horizontal above ground stem having nodes and long internodes. Leaves, flowers and roots may originate from the above ground nodes on the stolon, thus giving rise to new vegetative material. An example of a species having stoloniferous type growth would be that of bermudagrass. Again as with the rhizomes the stolons allow the plant to spread along the soil surface and fill in the intervening space. The primary difference between rhizomes and stolons would be the location of the stems. Rhizomes would be located below the soil surface and stolons would be located above the soil surface.

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Figure 13

This is an actual photograph of a stolon. The area labeled No. 1 would be the internodal region of the stolon and the area labeled No. 2 would represent the nodal area of the stolon. Note that leaves and roots are originating from the nodal regions of this stolon.

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Figure 14

This figure depicts another type of modified stem - the tuber. A tuber is a greatly enlarged short underground stem. An example of a species that has tuberous type growth would be that of the potato. The tuber itself is a stem and is greatly enlarged primarily as a result of containing large amounts of carbohydrates or starch. Also note the eyes or the buds located on the tuber. These eyes, or buds, are located at the nodes and give rise to new vegetative growth or plants. In fact, when potatoes are planted, the use of seed pieces are nothing more than portions of the tuber that contain one or two eyes or buds.

Figure 15

This figure depicts the next type of stem modification, which is referred to as a bulb. A bulb is also a modified stem composed of closely packed modified fleshy leaves. An example of a species that has a bulb would be the onion plant. In referring to the figure it may be noted that at the bottom of the bulb is located the stem from which adventitious roots are developing. The bulk of the bulb is composed of these large fleshy leaves from which at the apical end an apical shoot may develop-hence giving rise to a new plant. When eating an onion the material that one is eating would be the fleshy leaves that are filled with carbohydrates. In bulb-type plants most of the stored carbohydrates are stored in the leaves and not in the stem itself as was the case for the tuber.