Observe the morphology and primordial structures of common plant stems with the naked eye and microscope. The stem is the central axial part of the plant body. Upright or creeping in water, the stem bears branches with meristematic cells at the tips for apical growth. The stem generally divides into two parts: short nodes and long internodes.
Source: Botany test guide second edition (Shihezi University, College of Bioengineering, Department of Plant Teaching and Research).
Operation method
Stem morphology and primary structure
Materials and Instruments
Monocotyledons Dicotyledons Move I . Basic Morphology of Stems Caveat 1. Observe the structure of leaf buds: leaf buds of walnut, peach, willow, etc. may also be taken for observation. 2. Observe the structure of flower buds: cotton, hibiscus, acacia, walnut and other flower buds, anatomical observation of its structural characteristics. 3. observation of mixed buds can also not do longitudinal dissection, directly from the outside to the inside of the stripped scales, leaves, to the last observation of the growth point of the part is the flower organ until. Observe the sprouting of mixed buds on the plant in the spring, and you can see the simultaneous development of branches and flowers and false inflorescences. You can also take pear, begonia, lilac mixed buds to do anatomical observation, note children their structural characteristics. 4. Observation of the cabbage leaf ball note its growth cone, leaf primordia, young leaves, axillary bud primordia. Young leaves, axillary bud primordia and lateral axillary buds. Note that there is no bud scale cover outside the cabbage leaf ball, if analyzed according to the structure, it should be a bare bud type. 5. In late fall, seedlings can be pulled from the wheat field for observation, and teachers can also make green specimens of seedlings of cereal crops with tillers for observation in other seasons of the laboratory class. 6. On either side of the growth cone, there are leaf primordia and young leaves, as well as axillary bud primordia between the axils of young leaves. Note their cellular characteristics and what type of tissue they belong to7. Note that the pea primordium is two-layered and the corn primordium is one-layered. Look carefully at the cells visible dividing; in what direction are they dividing and what is their significance? Within the primordium is a group of irregular cells called the protoplasts, and dividing cells can also be observed in this part. How does the direction of division of these cells differ from that of the primary set of cells, and what is the significance of their dividing cells for stem growth? For more product details, please visit Aladdin Scientific website.
1% ruthenium red solution Paraffin wax
Tweezers Magnifying glass Dissecting glass Scalpel Blade White paper Slide Coverslip Microscope
Take a branch (preferably with lateral branches) of a three-year-old poplar or walnut and observe its morphological features. (Figure) 
1. Nodes and internodes: The position on the stem where leaves are borne is called a node, and the part between two nodes is called an internode.
2. Terminal and axillary buds (lateral buds): The buds that are borne on the top of the branch are called terminal buds, and the buds that are borne in the axils of the leaves are called axillary buds, or lateral buds.
3. Leaf Scar and Leaf Trace: The scar left on the stem after the leaf has fallen off is called a leaf scar, and the dotted protuberance on the leaf scar is the trace left after the petiole breaks off from the vascular bundles in the branch, and is called a leaf trace.
4. Bud scale scar: It is the trace left after the bud scale is detached when the bud develops into a new branch. They are often arranged in a ring around the stem. The age of the branch can be determined from the bud scale marks.
5. lenticels: small crack-like holes on the surface of the stem, which are the ventilation structures between the stem and the outside world. Observe the branches of apples and pears, and pay attention to differentiate between its long and short branches. Long branches have long internodes, short branches have short internodes and grow very slowly, and - in general - fruit trees only bloom and bear fruit on short branches, so they are also called fruit branches. (Figure) 
II . Structure and Types of Buds
1. Methods of dissecting buds
Take a branch and firstly observe the position of various types of buds bearing on the branch and their characteristics, and then remove the buds with tweezers. Holding the bud in the left hand, the right hand with tweezers will peel off the bud from the outside to the inside layer by layer, lay it on a piece of white paper, and observe it with a magnifying glass. Another method is to use a razor blade to cut the bud into two longitudinally, and then observe the structure of the bud with a magnifying or dissecting lens.
2. Structure of leaf buds
Take a lilac branch, take the slender leaf bud with forceps, dissect the leaf bud longitudinally with a scalpel, and observe it with a dissecting microscope. You can see the growth point, leaf primordia, young leaves and axillary bud primordia. The outermost part is the bud scale.
3. Structure of flower buds
Take the forsythia flower buds to make a longitudinal cut and observe. There is no growth point in the center, but the various parts of the yellow flowers protrude, some have appeared obvious petals and stamens. However, the bud scales of forsythia are extremely easy to fall off.
4. Structure of mixed buds
Take the terminal bud on the short branch of apple to do longitudinal dissection. First of all, the dissected half of the bud scales peeled off, inside the hairy young leaves, with tweezers gently remove the young leaves, you can observe the size of the protuberance, which is part of the apple flower bud within the floral apparatus.
(1) According to the position of the buds on the branches
Fixed buds: terminal buds, axillary buds.
Indeterminate buds: buds other than terminal buds and axillary buds. Buds other than axillary buds.
(2) Anatomy of the cabbage leaf bulb
Take a cabbage leaf ball (a very large bud) and cut it into two with a knife. The bud axis can be seen as a shortened
The stem, which is clustered with a lot of fat leaves, the young leaves rolled inward curved to form the center of the leaf ball, the real
The young leaves are curved inward to form an encapsulated leaf bulb, which is actually the terminal bud.
According to the nature of the buds: in the pre-winter is generally leaf buds, axillary buds often do not develop. After the New Year, the terminal buds open
After the New Year, the terminal buds begin to differentiate into inflorescences and floral primordia, and the entire leaf bulb becomes a mixed bud.
(3) Types of buds
1) By the position of the buds on the branches
Fixed buds: terminal bud, axillary bud.
Indeterminate buds: buds other than terminal buds. Buds other than terminal buds and axillary buds.
2) By nature
Leafy buds: contain several layers of young leaves that can develop into branches.
Flower buds: contain calyx, corolla and androgynophore, etc., and can develop into flowers or inflorescences.
Mixed buds: contain both leaves and flowers, and can develop into both flowering and leafy branches.
3) According to structure
Scale buds: buds with scales on the outside of the bud.
Naked buds: buds not covered with bud scales.
III . Observations on stem branching and tillering in graminaceous plants.
The phenomenon of plant branching is common in plant growth, the elongation of the main stem and the formation of lateral branches are the result of the development of terminal and axillary buds respectively. Lateral branches, like the main stem, also have their terminal and axillary buds, so the lateral branches can continue to produce new secondary lateral branches, and so on, forming the plant's branch system. Since the buds of various plants differ in their nature and law of activity, they produce branches in different ways. But branching is regular. Seed plants are generally branched in a uniaxial, coaxial and pseudo-bifurcate manner. However, graminaceous plants branch in the form of tillers.
1. Observing the trunks of Populus tremula and Pinus sylvestris and their branches in the campus, it can be found that the trunks of these trees, i.e., the main axes, are formed by the shoots of the tops of the mountains stretching upward continuously, and this kind of branch is called the uniaxial branch, or also called the racemose branch.
2. Observe the main trunks of apple, peach, sycamore, tomato, etc. The terminal buds do not develop into stunted growth during the growing season, and in some cases the terminal buds are flower buds, so that the terminal buds of such plants do not continue to develop into the main axis. Instead, lateral branches developed from axillary buds under the terminal buds grow upward instead of the terminal buds to develop into the main stem. The main stem of these plants is formed by the union of many lateral branches developed from the axillary buds, so it is called a coaxial branch.
3. In some plants with opposite leaves, the terminal bud usually stops growing, and some terminal buds are flower buds. The axillary buds on both sides of the terminal bud develop into bifurcate branches at the same time, so they are called pseudobifurcate branches. In fact, it is also a variation of the meristematic branching. Such as lilacs, elderberries and so on. 
4. Tillers of Gramineae
Gramineae plants have a special way of branching, these plants in the seedling stage, several stem nodes are crowded at the base, which is called "tiller node" in cultivation, and each node has axillary buds. When the seedling reaches 4-5 leaves, the earliest axillary buds become active and grow rapidly into new branches, followed by the emergence of adventitious roots at the nodes, which is called tillering. 
5. Structure of the stem tip
The stem tip is basically similar to the root tip, and also consists of three parts: meristematic zone (growth cone), elongation zone and maturation zone. But mainly observe the meristematic zone. Take a longitudinal section of a lilac stem tip or a boxwood stem tip and observe it (Fig.) The apical part of the growth cone of the stem tip is the proto-hyphal tissue; they can continuously produce new cells backward. These cells continue to divide on the one hand, and on the other hand initially differentiate into primary meristematic tissues; i.e., proto-epidermis, basic meristematic tissues, and proto-formative layer.
(1) Proto-epidermis: the outermost layer of smaller cells, neatly arranged, which later forms the epidermis of the stem.
(2) Basic meristematic tissue: within the primary epidermis. The cells are larger and less regularly arranged. It later develops into the basic tissues of the stem, i.e., cortex and pith.
(3) Protoplast: in the basic phloem, there are two bundles of elongated and deeply stained cells; it is the protoplast. Later it can further differentiate into the vascular bundles of the stem.
(4) Observation of protoxylem - protoxylem: Longitudinal sections of pea and corn stem tips were taken. From these sections, it can be observed that the outermost cells of the stem tip meristematic tissue are closely and neatly arranged, which is the primary set of cells. 
6. Primary structure of stem
(1) Primary structure of stems of dicotyledonous herbs
A paraffin section of a sunflower seedling or a branch end is made through the mature area of the stem tip. Observe the cross section. The primary structure of the young stem consists of three parts: epidermis, cortex and vascular column.
1) Epidermis: Epidermal cells are developed by cell division and differentiation from the original epidermis. Epidermal cells are small, only one layer, tightly arranged, the outer wall of the cell can be seen with keratinized cuticle. Some epidermal cells were transformed into epidermal hairs, either unicellular or multicellular. Observe the defense cells of the epidermal stomata of young stems with high magnification, the cross section of this cell is smaller than the general epidermal cells, and the pore slit between the two defense cells and the cavity inside them can also be seen, which is called the sub-pore chamber. The cell structure of this layer can be observed by freehand sectioning, and the structure of epidermal hairs will be clear.
2) Cortex: It is the part within the epidermis and outside the vascular column, and the cells in this part are differentiated from the basic meristematic tissue. Several layers of cells near the epidermis are relatively small and are thick angular tissues, with cells thickening at the corners. If fresh young sunflower stems are cut by freehand sectioning, chloroplasts can be observed in the cells of the thick angular tissue. A drop of fresh 1% ruthenium red solution also shows that the intercellular layer between each thick horn cell is stained red, so that the thickening at the corners is clearly visible. Inside the thick horn cells are several layers of book-walled cells, i.e. the basic tissue. In the basic tissue there is a secretory cavity surrounded by secretory cells (which should be secretory tissue). The innermost layer of cells in the cortex is called endothelial cells. When observed under high magnification, Kjeldahl points can be observed on individual cells of the endodermis. However, the endothelial cells of other herbaceous stems are not thickened with Kjeldahl bands and contain more starch granules called starch sheaths. If the young stems of broad bean or dahlia are cut crosswise with bare hands and stained with sulfur solution, the starch granules in the starch sheath can be observed directly.
3) Vascular Column: It is relatively developed. The vascular column of young sunflower stems has a large area compared with the root primordium and all parts of the inner cortex. However, the inner cortex and the mid-column sheath cells are very inconspicuous, making it difficult to distinguish the vascular column from the cortex. When observed under a low-power microscope, the vascular column of the stem can be divided into three parts: the vascular bundles, the medullary rays, and the pith.
A. Vascular bundles: Mostly bundled, many vascular bundles are arranged in a ring in the transverse section, stained darkly and easily recognized. Each vascular bundle is composed of incipient phloem, intrafascicular formation layer and incipient xylem. Moreover, the phloem is outside the xylem and is the outer phloem vascular bundle, which is also known as the infinite vascular bundle due to the presence of the intrafascicular formation layer. They all develop from the primary formation layer.
Primary phloem: Includes primary phloem and posterior phloem, which matures from the outside inward during development, so it is called the outer initiating form. In sunflower, the outermost part of the vascular bundle is the primary phloem fiber, which is also called the "middle column sheath fiber". Inside the bast fibers are sieve tubes, companion cells and bast thin-walled cells. For detailed observation, the objective lens should be switched to high magnification. Intrafascicular formation layer: It is the phloem tissue retained from the original formation layer that still has the ability to divide. In cross section, the cells are flattened and thin-walled.
Primary xylem: Includes the primary essential part and the posterior xylem. According to the size of the caliber of the conduit molecules and the depth of the saffron staining can be judged, close to the center is the primary xylem, and its outer side is the posterior xylem. During development, the primary xylem is differentiated and matured from the inside out. Therefore, it is called endogenous. When observed under high magnification, attention should be paid to identifying the four components of ducts, tubular cells, hydrofibroblasts and wood-thin-walled cells (refer to the longitudinal slice of sunflower stems or dissociated material, when available, for observation).
B. Pith rays: These are thin-walled cells that exist between the two vascular bundles, connecting the cortex with the pith in the center of the stem, and transporting substances between the pith and the thin-walled cells of the cortex, as well as serving as storage, and are derived from the basic meristematic tissues between the original lamina bundles.
C. Pith: The thin-walled cells located in the center of the stem and also in the center of the vascular column are loosely arranged and often have a storage function. It is developed from the basic meristematic tissue.
(2) Primary structure of young cotton stem
Cotton is a dicotyledonous plant and its stems are water-textured herbaceous stems. Sections of young cotton stems can also be taken to observe the primary structure. 
(3) Primary structure of dicotyledonous woody stems
Young stems of the genus Pear or Peach are observed in cross-sectioned sections. Take the mature area of the pear or peach stem tip for permanent sectioning or make freehand sections for observation.
The basic structure is similar to that of herbaceous stems.
1) Epidermis: living cells located in the outermost layer of young stems. The cells are regular in shape, closely arranged, with no intercellular space, and the outer wall is keratinized, forming a cuticle with epidermal hairs and a few stomata.
2) Cortex: Located in the inner epidermis, it consists of several layers of living cells. The cells close to the epidermis are thick horny tissue, which can increase the mechanical support of young stems. Cortical cells are generally larger, loosely arranged, with intercellular space, the cells contain chloroplasts, photosynthesis, so generally young stems appear green. Peach young stem cortex of the innermost layer of cells containing starch granules, also known as starch sheath. Some cells in the cortex of young peach stems contain tannins.
3) Vascular column: The vascular bundles, medullary rays and pith are first distinguished under low magnification. The vascular bundles are tightly arranged in a ring-like pattern within the vascular column, and the medullary rays between the bundles are narrower and less obvious. Developing into vascular bundles from the primary formation layer, the formation layer is evident in the bundles, which are lined with incipient phloem on the outside and incipient xylem on the inside. The vascular bundles of the stems of both the peach and pear genera are externally tough vascular bundles.
The cellular characteristics of the components of the vascular bundle were observed under high magnification. 
(4) Stem structure of monocotyledonous plants
Monocotyledonous and dicotyledonous stems differ in many ways. Most of the monocot stems have only primary structures, so the structure, is relatively simple; a few have secondary structures, but they are also different from the stems of dicot plants. The stems of graminaceous plants are used as a representative to observe the structural characteristics of monocotyledonous stems.
1) Structure of corn stem
A cross-section of a corn stalk is taken for observation.
A. Epidermis: The outermost layer of cells in the stem is the epidermis. The transverse section is flat and square, neatly arranged, with thickened outer wall, some cells are smaller, with shiny siliceous thickening on the wall. There are stomata on the epidermis, and the very small cells that can be observed in the transverse section are guard cells. Next to the defense cells are larger paracells. Fresh material can be used to scrape the epidermis of young corn stems directly to make clinical slices, and observe the cell structure of the epidermis: a long cell, two short cells and stomatal apparatus can be seen in the epidermis of corn stems in a regular arrangement. The long cells have keratinized outer walls, and these long cells make up most of the epidermis. The two types of short cells, one with a pegged outer cell wall and the other with a silica cell containing silicon trioxide in the outer cell wall, are located between the long cells. In addition, there are dumbbell-shaped defense cells and stomatal apparatus formed by paracells on the epidermis, but they are few in number and sparsely arranged. (Figure)
B. Basic Organization: In mature stems, near the epidermis, there are 1-2 layers of cells closely dissected and small in shape, which are thick-walled cells forming the outer cortex. They are arranged in a protective bad, interrupted at regular intervals by stomatal zones, which are connected to the air cavities below the stomata. Inside the thin-walled basic tissue cells, the cells are larger, loosely arranged, and there are cell gaps. The closer to the center of the stem, the larger the cell diameter.
C. Vascular bundles: In the basic tissue, there are many scattered vascular bundles. The vascular bundles are more numerous at the edges of the stem, where each bundle is smaller, and less numerous in the central part of the stem, where each bundle is larger. As a result, there is no clear boundary between the cortex, vascular column and pith in the corn stalk.
The corn stalk vascular bundle is wrapped in a sheath of thick-walled tissue (fibers). Inside, there are only two parts, the primary xylem and the primary phloem, with no intervening lamina. The primary xylem usually contains 3-4 conspicuous ducts, which are arranged in a groove cut in the shape of a V. The lower half of the V is the primary xylem, which contains 1-2 smaller ducts and a small number of thin-walled cells. Inside the small ducts there is a large cavity, formed by the destruction of part of the earliest-formed primary xylem. Generally this cavity extends along the vascular bundle and forms an airway within the stem. v The upper half of the v-shape is the posterior xylem, containing two large pore-spinning ducts, and between the two, a number of tubular cells are distributed - some tubular cells. Outside of the primary xylem is the primary phloem, of which the primary phloem is located on the outside of the primary phloem, but has been destroyed by extrusion, and some residual remains can sometimes be seen. The posterior phloem, which is the effective part of the primary phloem, contains only two components, sieve tubes and companion cells, and is usually devoid of phloem thin-walled cells and other components. 
2) Structure of wheat stem
Take a cross-sectioned preparation of wheat stem for observation (Fig.) Note the comparison with corn stems. 
A. Epidermis: The cells of the epidermis layer have two types of epidermal cells besides stomatal apparatus, one narrow and the other of equal diameter.
B. Mechanical and Green Tissues: the mechanical tissues located under the epidermis are thick-walled cells that form continuous zones of varying thicknesses on the inner side of the epidermis that surround the green tissues as well as smaller vascular bundles on the periphery. The green tissue consists of thin-walled cells that are rounded in cross-section and longitudinally induced, and the air chambers below the stomatal apparatus are often connected to the green tissue. However, note that the green tissue is less, or even completely absent, in the basal internodes of the stem.
C. Basic tissue: within the mechanical tissue up to the central medullary cavity, are composed of thin-walled cells, near the medullary cavity is larger.
D. Vascular bundles: The vascular tissue of the internodes consists of two rings of vascular bundles. The outer ring of small vascular bundles interacts with the green tissue. The inner ring of vascular bundles is located in the thin-walled cells of the basic tissues and is the outer tough vascular bundle. Its specific structure is similar to that of corn stems.