Stem and Shoot

The main function of a green shoot is the production of organic substances from inorganic ones using light energy. This process occurs in leaves — specialized lateral organs of the shoot that contain chlorophyll. The flat shape of the leaf blade provides a maximum surface area per unit volume of tissue, which aids in efficient light capture and gas exchange (Mauseth, 2017). The stem, by bringing leaves to the light, optimizes conditions for photosynthesis. Young green stems with chlorenchyma beneath the epidermis also actively participate in photosynthesis (Andreyeva, Rodman, 2002).

The shoot connects the two other main plant organs — the root and the leaves. Two‑directional transport occurs along the stem:

Thus, the shoot serves as the plant’s central transport highway.

The stem holds leaves, flowers, and fruits in an optimal position relative to light, air, and pollinators. This function is provided by:

Thanks to the supportive function, shoots of many plants reach considerable heights (over 100 m in sequoias), while climbing shoots (lianas) use other plants as support.

The shoot is the most important organ for natural and artificial vegetative reproduction. Many plants produce specialized shoots for dispersal and formation of new individuals:

All these structures are easily distinguished from roots by the presence of buds and leaf scars.

Reserve nutrients (starch, oils, proteins) can be deposited in shoots. This function is particularly pronounced in modified shoots (tubers, bulbs, rhizomes), but even in ordinary stems, the parenchyma of the pith and cortex often contains reserves (Andreyeva, Rodman, 2002). For example, sucrose accumulates in sugarcane stems, and starch in the pith of palms.

The shoot participates in gas exchange (oxygen, carbon dioxide) and regulated water evaporation (transpiration). Stomata, located on leaves (and sometimes on young stems), allow CO₂ to enter for photosynthesis and O₂ to be released, and also create a suction force necessary for water rise through the xylem (Graham et al., 2014). Transpiration also cools leaves and facilitates the uptake of mineral elements from roots.

Flowers and inflorescences, and subsequently fruits and seeds, form on shoots. Thus, the shoot bears the organs of sexual reproduction. In this regard, part of the shoot system is transformed into flowering shoots, which may differ greatly from vegetative ones (Bell, 1991).

Shoots, especially their apical meristems and young leaves, synthesize phytohormones (auxins, gibberellins, etc.) that regulate growth, development, and tropisms of the whole plant. These substances influence apical dominance, branching, cambial activity, and other processes (Evert, 2006).

Thus, the shoot is a polyfunctional organ that integrates aerial nutrition, transport, support, reproduction, and signaling. Understanding these functions is necessary for further study of stem and leaf anatomy and morphology.

One of the key features of the shoot is its metamerism, i.e. a jointed structure consisting of repeating units — metameres (Serebryakova et al., 2006). Each metamere includes:

In most plants, nodes are well visible (e.g. in grasses, bamboo), while internodes can be greatly elongated (birch, sunflower) or, conversely, very short — then leaves are gathered in a basal rosette (dandelion, strawberry) (Andreyeva, Rodman, 2002).

The stem is the axial part of the shoot that bears leaves and buds. Its main external characteristics:

The leaf is a lateral vegetative organ that is generally flat and has limited growth. Main parts of a leaf:

Leaves can be sessile (without petiole) and petiolate. According to blade shape, degree of dissection, and venation, a huge diversity exists, used in systematics (Mauseth, 2017).

A bud (gemma) is an embryonic, yet unexpanded shoot. It consists of a short axis with a growing tip and young leaves (or flowers). Externally, the bud is often covered with bud scales — modified leaves that protect the meristem from desiccation and mechanical damage (Evert, 2006).

Classification of buds:

Based on presence of protection, we distinguish closed buds (with scales) and naked buds (characteristic of many herbaceous plants).

The order of leaf placement on the stem is called phyllotaxis. It is a heritable trait of a species and important for maximizing light capture.

Three main types are distinguished (Andreyeva, Rodman, 2002; Mauseth, 2017):

For alternate phyllotaxis, one can calculate the divergence angle (shift) between adjacent leaves; it often equals 1/2, 1/3, 2/5, 3/8, etc., of the stem circumference, described by the Fibonacci series and ensuring minimal self‑shading (Bell, 1991).

Branching is the formation of a system of shoots from axillary buds. It allows the plant to increase its photosynthetic surface and occupy aerial space.

Two main types of branching are distinguished (Serebryakova et al., 2006):

A special case is tillering in grasses: branching occurs at the base of the shoot, in the tillering zone, where numerous lateral shoots are formed (Graham et al., 2014).

In some plants, leaves on the same shoot may differ in shape, size, and even function. For example, in arrowhead (Sagittaria), submerged leaves are ribbon‑like, floating leaves are arrow‑shaped, and aerial leaves are broad with an arrow‑shaped base. In mulberry, entire and lobed leaves occur on the same tree. Heterophylly is often associated with age‑related changes (juvenile and adult leaves) or light conditions (Mauseth, 2017).

Thus, the external structure of the shoot reflects its metameric nature and diversity of adaptations. Knowledge of shoot morphology is necessary for plant identification, understanding their growth, and application in agronomy (crown shaping, methods of vegetative propagation). In the next section, we will examine the anatomy of the stem.

In a young herbaceous stem of a dicot (e.g., sunflower, clover), the following zones can be distinguished in cross section (Andreyeva, Rodman, 2002):

3.1. Pericycle — one or several layers of cells adjacent to the endodermis. In stems, the pericycle is often represented by sclerenchyma fibers (bast fibers) or parenchyma.

3.2. Vascular bundles (vascular‑fibrous bundles) — arranged in a ring (in dicots). Each bundle (open collateral) includes:

In monocots (maize, tulip), vascular bundles are closed (cambium absent) and scattered throughout the stem cross‑section without a clear separation into cortex and pith (Graham et al., 2014).

Depending on the arrangement of vascular tissues, several types of stele are distinguished, reflecting evolutionary complexity:

Primary structure forms as a result of apical meristem activity and is typical of young (herbaceous) stems, as well as annual shoots of perennials. In the primary cortex and pith, living parenchyma is retained, and mechanical tissues are represented by collenchyma and small groups of fibers.

Secondary structure arises due to the activity of the cambium (lateral meristem) and is typical of perennial trees and shrubs (Evert, 2006). The cambium deposits secondary xylem (wood) to the inside and secondary phloem (bast) to the outside. As a result:

Thus, the perennial trunk of a tree in cross section shows a clear zonal structure: externally — bark (periderm and dead cortex), beneath it a thin layer of living phloem, then cambium, a large part — wood (xylem) with annual rings and radial medullary rays, and in the center — pith or a cavity (Bell, 1991).

In monocots (grasses, lilies, palms), cambium is absent, so no secondary thickening occurs. Vascular bundles are closed (without cambium) and scattered throughout the stem thickness. Strength of grass stems is achieved by:

In palms and some other monocots (Dracaena, Yucca), secondary thickening occurs via a special accessory cambium (primary thickening meristem), which forms in the peripheral part of the stem and gives rise to new vascular bundles and parenchyma (Andreyeva, Rodman, 2002). This thickening is called diffuse (in contrast to the ring‑like thickening in dicots).

Collenchyma — living mechanical tissue, typical of young herbaceous stems and leaf petioles. It is elastic, allowing the stem to bend without breaking.

Sclerenchyma — dead fibers with lignified thick walls; provide rigidity and resistance to compression. Particularly developed in stems of grasses, flax, hemp.

Parenchyma — ground tissue, performs storage, sometimes photosynthetic functions. In succulent stems (cacti, euphorbias), parenchyma serves for water storage.

Thus, the anatomical structure of the stem fully corresponds to its main tasks: transport of water and organic substances (xylem and phloem), support (collenchyma, sclerenchyma, lignified xylem walls), protection (epidermis, periderm), storage and gas exchange (parenchyma, stomata, and lenticels). Understanding the internal structure is necessary for plant identification, studying their growth, and for practical purposes such as determining wood quality, breeding varieties with strong stems (resistant to lodging), and for rational pruning and crown shaping.

In the next section, we will consider the classification of shoots by growth direction, spatial position, and types of metamorphosis.

Based on growth direction relative to gravity, we distinguish (Serebryakova et al., 2006):

Elongated shoots — have well‑developed, often long internodes, bearing leaves spaced far apart. They provide growth and space occupation.

Shortened shoots — internodes are strongly contracted, leaves clustered in a rosette or whorl. They often serve as a perennial photosynthetic surface (pine needles, plantain rosettes, apple “fruit spurs”). In many trees, both types occur on the same plant (e.g., in larch — elongated shoots with single needles and shortened shoots with needle clusters) (Mauseth, 2017).

Herbaceous shoots — do not become woody (or only weakly so), live for one growing season (annuals) or several years with annual dieback of the above‑ground part (perennial herbs). Their stems contain little lignin, mechanical strength is provided by turgor and collenchyma.

Woody shoots — perennial, heavily lignified, possess cambium and secondary tissues. The main stem of a tree is called the trunk, in shrubs — stems (or caudices). They are capable of perennial growth and annual thickening.

Under the influence of special environmental conditions and in connection with performing specific functions, shoots can be greatly modified. Metamorphosis is a heritable change in the form and structure of an organ caused by a change in function (Serebryakova et al., 2006). Aerial and underground shoot metamorphoses are distinguished.

For an agronomist, it is important to distinguish between underground metamorphoses of shoots and roots.

These differences have practical significance: for potato propagation, pieces of tuber with buds are used, whereas for carrot (a taproot) this is useless — seeds or the apical part with buds are needed.

Thus, the diversity of shoots reflects the richness of higher plant adaptations. Knowledge of classification and types of metamorphoses is necessary for plant identification, developing weed control methods, vegetative propagation, and proper crop care (pruning, shaping, hilling).

In the next section, we will examine shoot ontogeny — how it develops from a bud and how its tissues form.

A bud is an embryonic shoot in which future leaves and internodes are in a highly compressed state. As soon as favorable conditions arrive (in spring or after a dormant period), the bud “unfolds”:

In many plants, internodes do not grow uniformly along the entire length but rather by intercalary (insertional) growth. This means that dividing cells are retained at the base of each internode (or at the base of the shoot) for some time. Intercalary growth is especially well expressed in grasses: the stem (culm) elongates rapidly due to cell division at the base of each internode, even if the apical meristem has already switched to inflorescence formation (Graham et al., 2014). This allows grasses to recover quickly after mowing or grazing.

Depending on how long the apical meristem functions and how the main axis is replaced, two main types of shoot increment are distinguished (Serebryakova et al., 2006).

Differences in increment types have practical significance: when pruning fruit trees, the sympodial growth pattern is taken into account to stimulate the desired buds.

Branching is the formation of lateral shoots from axillary buds. It allows the plant to maximize the use of space and light.

Several branching patterns are distinguished based on the position of the strongest branches on the mother axis (Mauseth, 2017):

Practical significance: in cereals, tillering increases yield; when growing flax and hemp, on the contrary, weak branching is desired (single‑stem plants produce longer, higher‑quality fiber).

The apical (terminal) bud produces auxin, which suppresses the growth of axillary buds. This phenomenon is called apical dominance. Thanks to it, the main shoot grows faster than lateral ones, and the crown acquires a characteristic shape (spruce, poplar). If the apical bud is removed (pinched), dominance is lifted, and lateral buds begin to grow, leading to tillering or branching. This principle is widely used in agronomy:

In perennial plants, many axillary buds remain unexpanded for years, staying dormant. They remain viable because their apical meristem produces a few new embryonic metamers each year, while the outer scales fall off (Serebryakova et al., 2006). Dormant buds become activated when the trunk is damaged or when the crown ages, giving rise to water sprouts (epicormic shoots). This is significant for rejuvenation pruning.

Adventitious buds arise on internodes, leaves, or roots from deeper tissue layers (pericycle, cambium, parenchyma). They give rise to shoots in unusual places, which is used in cuttings and for controlling root‑suckering weeds (sow thistle, bindweed).

In perennials, a shoot may go through successive phases during its life: juvenile (young, often with heterophylly), adult vegetative, and generative (flowering). The transition to flowering is associated with a transformation of the apical meristem — it stops producing leaf primordia and begins to form flowers or inflorescences. In agronomy, it is important to note that for some plants (winter cereals, biennials), exposure to low temperatures (vernalization) is required for flowering, which is used in breeding and seed production (Evert, 2006).

Thus, shoot ontogeny is a dynamic process that includes unfolding from a bud, intercalary growth, branching, and interaction between apical and axillary meristems. Knowledge of these mechanisms allows purposeful management of plant growth.

In the next section, we will briefly consider environmental factors affecting shoot function.

Light is one of the primary factors affecting the shoot. Its impact is multifaceted:

Temperature affects the rate of all growth processes and seasonal rhythms:

Water is a critical resource for the shoot:

Availability of mineral elements, especially nitrogen, phosphorus, and potassium, strongly influences shoot morphology:

The shoot exhibits negative gravitropism — it grows upward, against gravity. Statoliths (starch grains in endodermal or cortical cells) settle on the lower side of the cell, triggering auxin redistribution that causes upward stem bending (Evert, 2006). This mechanism is important for maintaining vertical stem position and optimal leaf orientation.

Mechanical loads (wind, rain, touch) can influence shoot growth. Regular swaying leads to shorter internodes, thicker stems, and enhanced development of mechanical tissues. This is used in seedling production: gentle brushing or fanning makes plants more compact and resistant to lodging (Mauseth, 2017).

Damage (tip breakage, animal browsing) removes apical dominance and stimulates branching. In agronomy, this is used to shape bushes in ornamental and fruit crops.

In perennial plants, shoots enter a dormant state (dormancy) in response to shortening day length and decreasing temperatures in autumn. Dormancy may be imposed (ends when favorable conditions return) or organic (deep dormancy requiring prolonged chilling) (Serebryakova et al., 2006). Knowledge of dormancy depth is important for forcing crops in greenhouses and assessing variety winter hardiness.

In nature, factors act together. For example, etiolation (elongation in darkness) is reversed even by weak light. Drought exacerbates the effect of high temperature. Fertilizers are effective only when sufficient moisture is present. Therefore, in agronomy, a comprehensive consideration of environmental conditions is necessary to optimize shoot growth and achieve high yields.

Thus, external factors not only limit but also actively shape shoot morphology and physiology. Their knowledge underlies crop management practices (planting dates, irrigation, fertilization, pruning, crown shaping, frost protection).

In the next section, we will consider the relationship of the shoot with other plant components — the root and leaves.

Above‑ground and underground parts of a plant are in constant interaction. Simplified, we can say that the root feeds the shoot, and the shoot feeds the root, but in reality the connections are more complex (Evert, 2006).

These connections ensure growth coordination: the root‑shoot balance (ratio of root mass to shoot mass) is usually maintained within certain limits. When roots are damaged (e.g., during transplanting), shoot growth slows. Conversely, when part of the shoot is removed (pruning), root development may increase because the demand for water and minerals decreases, and stored carbohydrates are directed to roots.

Energy supply: Roots themselves do not photosynthesize, so their growth and activity depend on the supply of organic substances from leaves. Weakening of photosynthesis (shading, leaf removal, leaf surface damage) leads to inhibition of the root system.

Formation of adventitious roots: In many plants, adventitious roots form on stems (at nodes, sometimes at internodes). This provides additional anchorage and nutrition, especially in creeping, trailing, and climbing forms (ivy, strawberry, maize) (Bell, 1991).

Root suckers: Some plants produce adventitious buds on roots (root suckers), which develop into independent shoots (sow thistle, raspberry, aspen). Here, the shoot arises under the influence of signals from the root.

Water regime and mineral transport: When water is scarce in the soil, roots cannot supply transpiration, and the shoot loses turgor, wilts. With excess water (flooding), roots suffocate, which also affects the shoot. Deficiency of mineral elements manifests as chloroses, necroses, leaf and stem deformations.

Regulation of branching and growth: Root‑derived cytokinins affect the awakening of axillary buds, stimulating branching. When part of the roots is removed (transplanting, cultivation), cytokinin supply to the shoot may temporarily decrease, delaying growth and development (Graham et al., 2014).

Stress signaling: During drought, salinity, or pathogen attack, roots produce abscisic acid (ABA), which travels via xylem to leaves and causes stomatal closure, reducing transpiration. Thus, the root “warns” the shoot of unfavorable conditions.

The leaf is not a separate organ but an integral part of the shoot. Their relationship is evident in:

Thanks to the interconnection of all organs, an integrated transport network is formed:

Thus, the shoot, root, and leaves form a single functional system; disruption of any part affects the whole plant. In agronomy, this is taken into account when applying fertilizers (foliar and root), pruning, hilling, irrigation, and plant protection.

In the next section, we will consider practical shoot management and the applied value of this knowledge.

Apical dominance (suppression of axillary bud growth by the apical bud) is a key phenomenon used in agronomic practices (Evert, 2006).

Shoot metamorphoses and regenerative capacity are widely used for vegetative propagation:

Many perennial noxious weeds (couch grass, sow thistle, ground elder, field horsetail) propagate by underground shoots — rhizomes, as well as root suckers (sow thistle). Knowledge of the morphology of these organs is essential for effective control:

Wood (xylem) — a highly valuable material obtained from perennial shoots of trees and shrubs. Wood properties (density, hardness, texture) depend on stem anatomy (ratio of vessels, tracheids, fibers, parenchyma, presence of annual rings). Anatomical knowledge is necessary for sorting wood by purpose (construction, furniture, paper, musical instruments) (Evert, 2006).

Bast fibers (flax, hemp, nettle, jute) — are sclerenchyma fibers of the phloem (bast) of the stem. Their length, strength, and elasticity are determined by anatomy. To obtain long, little‑branched stems (and high‑quality fiber), flax and hemp are grown at high density, without pinching.

Shoots as vegetables and spices: asparagus (young shoots), white cabbage (head — a giant terminal bud), Brussels sprouts (axillary buds), broccoli (flowering shoots), garlic and onion (bulbs), ginger (rhizome).

Cork is produced by cork cambium (phellogen) in the bark of perennial shoots of cork oak. Its unique properties (waterproofness, elasticity) result from the structure of cork cells.

By manipulating the shoot, the transition to the generative phase can be regulated:

Winter covers, snow retention, whitewashing trunks (to protect from sunscald and frost cracks) — all aim to preserve shoot buds and cambium.

Irrigation and fertilization must account for the above‑ground/underground balance: excess nitrogen leads to loose, lodging shoots susceptible to diseases; phosphorus and potassium strengthen mechanical tissues and increase stress resistance.

Growth retardants — substances that inhibit internode elongation — are used to produce compact, lodging‑resistant seedlings (wheat, flower crops) (Mauseth, 2017).

The shoot is a complex and dynamic organ that integrates the functions of support, transport, photosynthesis, and reproduction. Its metameric structure, ability to branch and undergo various metamorphoses, as well as its close connection with root and leaves, ensure the remarkable plasticity of higher plants. Knowledge of shoot biology underlies many agronomic practices — from orchard pruning to weed control and breeding new varieties. Understanding the internal structure of the stem and growth mechanisms enables humans not only to use plants but also to purposefully manage their development, increasing productivity and resilience of agroecosystems.