PLANT ANATOMY - Y.I. Korniievskyi - 2017

Lecture Notes

Lecture No. 4. ANATOMY OF VEGETATIVE ORGANS. SHOOT. STEM

Lecture Outline

1. Types of branching and modes of SHOOT growth.

2. Shoot metamorphosis.

3. Bud.

4. Water/140.html">Anatomical Structure of stems in monocotyledonous plants.

5. Anatomical structure of stems in dicotyledonous plants.

6. Anatomical structure of stems in woody angiosperms and gymnosperms.

7. Anatomical structure of rhizomes.

8. GENERALIZED SCHEME OF the histological composition of axial plant Organs (rhizomes and stems of woody plants).

9. Generalized scheme of the histological composition of axial plant organs (roots and stems of herbaceous plants).

The shoot (Cormus) is a leafy-stemmed vegetative organ of higher plants that provides aerial Nutrition, Vegetative Reproduction, and is capable of metamorphosis. The constituent elements of a shoot are the stem with nodes and internodes, buds, and leaves.

The Characteristic Features of a shoot include:

✵ indeterminate growth and initiation of new organs due to meristem activity;

✵ radial Symmetry (several planes directed along the radius can be drawn);

✵ longitudinal symmetry, or metamerism – the sequential repetition along the axis of a metamer: a node, a leaf, an axillary bud, and the underlying internode.

The main shoot, or first-order axis, is laid down in the sporophyte embryo of higher plants. During seedling development, subsequent metamers of the main shoot are formed by the apical bud, while lateral buds give rise to shoots of the second and higher orders.

Depending on the degree of branching, shoots can be unbranched (columnar stem – aloe, palms), weakly branched, and heavily branched.

1. Types of branching and modes of shoot growth:

- apical branching and dichotomous or forked growth – the main axis ceases growth early, the apical meristem bifurcates, producing a pair of lateral axes that subsequently branch equally or unequally;

- lateral branching – shoots are formed from lateral buds located below the growing point of the main axis;

- monopodial type – the apical bud ensures the progressive growth of the main axis, while lateral axes are less developed and do not surpass the main axis;

- sympodial growth – the apical bud ceases its development, and a lateral shoot of the second order develops from the nearest lateral bud, growing in the direction of the main axis and seemingly replacing it;

- tillering - The Development of lateral shoots from the Base of the main axis.

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1-2 - apical branching, dichotomous growth (equal and unequal forking); 3-5 - lateral branching, monopodial growth with alternate (3), opposite (4), and whorled (5) arrangement of lateral axes; 6-8 - lateral branching, sympodial growth of the following types: monochasium (6), dichasium (7), pleiochasium (8).

1 - dichotomous; 2 - monopodial; 3 - sympodial; 4 — pseudodichotomous; 5 — tillering; a — loose; b — dense; c — rhizomatous.

· Crown - The system of shoots (branches) that defines the overall appearance (habitus) of a tree.

· Vegetative aerial shoots:

- annual herbaceous assimilating shoots;

- perennial woody shoots or branches;

· By spatial orientation:

- vertical and horizontal.

✵ among vertical or orthotropic shoots, upright ones predominate;

✵ in lianas - plants incapable of maintaining an upright position in space - the shoots are twining, wrapping around a support (hops, beans, morning glories), or climbing/clinging due to various adaptations: holdfasts (wild grape), adventitious rootlets (ivy), tendrils (grape, pumpkin), hooks (bedstraw). Horizontal or plagiotropic shoots trail along the ground; some of these are procumbent or prostrate shoots that do not ROOT (knotweed, rupturewort), whereas creeping shoots take root (periwinkle, ground ivy).

2. Shoot Metamorphoses

Aerial Shoot Modifications

1 - runners (strawberry), 2 - aerial tubers (kohlrabi), 3 - tendrils (grape), 4,5 - axillary spines (hawthorn) and adventitious spines (honeylocust), 6 - part of a stem succulent - a cactus with a spherical succulent green stem and lateral wart-like areolae bearing spines instead of leaves, 7,8 - cladodes with hairs (Schlumbergera) and areolae (Opuntia), 9,10 - development of phylloclades (Asparagus), 11 - phylloclades with a flower (Ruscus).

Underground Shoot Metamorphoses

1-4 - rhizomes: 1 - monopodial, slender, elongated; 2 - sympodial, thickened, shortened, with scars from aerial shoots; 3 - tuberous, 4 - thickened, shortened, with tubers and tuberous roots; 5 - underground stolons with terminal tubers, 6 - corm, 7,8 - simple bulbs, 7 - tunicated, 8 - scaly. a - stem with nodes and internodes, b - adventitious roots, c - apical bud, d - thickened hypocotyl and lower internodes of a rosette shoot, e - basal plate, f - dry scales.

3. Bud (gemma)

A shoot primordium (bud) characterized by shortened internodes and a state of relative dormancy.

A bud consists of an embryonic stem with an apical meristem at the tip; leaf primordia; and embryonic lateral buds.

Functions of buds: ensuring the lengthwise growth of shoots, forming lateral branching shoots, and providing vegetative regeneration and propagation.

1 - vegetative closed bud of oak (general view and longitudinal section), 2 - generative closed bud of elderberry (general view and longitudinal section), 3 - vegetative-generative bud of cereals; a - apical meristem, b - leaf primordia, c - embryonic buds, d - bud scales, e - embryonic inflorescence.

The stem (caulis) is the axial, typically above-ground, radially symmetrical supporting part of the shoot. It develops from the embryonic stem, exhibits unlimited apical growth, and displays positive heliotropism. As a vegetative organ, it integrates all PARTS OF THE plant Organism. The stem connects the above-ground and underground organs; Supports and spatially orients the entire aerial mass; ensures both ascending and descending translocation of substances; assimilates while green; stores nutrients; and participates in vegetative propagation. The stem is metameric, as it consists of repeating units: nodes with leaves, buds, shoots, and internodes—the stem sections between two adjacent nodes. Shoot diversity is further enhanced by stem Morphology, including cross-sectional shape, color, and surface features (such as hairs, prickles, lenticels, and scales).

Stem cross-sectional shapes

a - cylindrical, b - elliptical, c - quadrangular, d - rounded-triangular, e - concave-triangular, f - four-angled, g - prismatic, h - polygonal, i - ribbed, j - rounded-ribbed.

4. Anatomical Structure of Monocot Stems

The structure of annual monocot herbaceous stems is primary and closed collateral bundle-type. The dermal tissue is the epidermis. The primary cortex may be entirely absent, though it most commonly consists of several rows of parenchyma. The central cylinder is characterized by the absence of secondary meristem (cambium) and the presence of closed collateral bundles. The pith is either morphologically indistinct or the stem is hollow (characteristic of a culm).

Fig. 4. Stems of monocotyledonous plants:

A - Secale cereale L.: 1 - under low magnification, 2 - under high magnification (fragment); B - Zea mays; C - Polygonatum multiflorum L.: 1 - epidermis, 2 - chlorenchyma or cortical parenchyma, 3 - pericyclic sclerenchyma, 4 - closed collateral bundle (a - phloem, b - xylem, c - bundle sheath sclerenchyma), 5 - ground parenchyma of the axial cylinder, 6 - culm cavity.

5. Anatomical Structure of Dicot Stems

In the apical meristem of the stem, just below the leaf primordia, the Differentiation of the primary cortex and pith begins, with a ring of residual meristem persisting between them. Numerous small or large bundles may form within it, or the bundles may merge into a continuous ring, which determines the specific structural type of dicot stems.

The Tissues of annual stems are grouped into two main regions: the primary cortex and the central cylinder. The dermal tissue is the epidermis. The primary cortex includes chlorophyll-bearing cortical parenchyma and storage parenchyma. The central cylinder may exhibit bundle, transitional, or non-bundle structural types. The stem pith can be solid, homogeneous or heterogeneous, or hollow.

Fig. 5. Stem of an herbaceous dicot plant with bundle-type structure — Cucurbita pepo L.:

A - under low magnification; B - under high magnification (fragment): 1 - epidermis, 2 - angular collenchyma, 3 - cortical (chlorophyll-bearing) parenchyma, 4 - tricyclic sclerenchyma, 5 - bicollateral bundle, 6 - pith ray, 7 - pith with a cavity.

Fig. 6. Stem of an herbaceous dicot plant with bundle-type structure — Trifolium pratense L.

1 - epidermis, 2 - cortical parenchyma, 3 - open collateral bundle, 4 - pith ray, 5 - pith.

Fig. 7. Stem of a herbaceous dicotyledonous plant of the transitional type, Helianthus annuus L.:

A - at low magnification, B - at high magnification: 1 - epidermis with trichomes, 2 - collenchyma, 3 - cortical parenchyma, 4 - schizogenous duct, 5 - endodermis, 6 - open collateral bundle (a - sclerenchyma, b - phloem, c - cambium, d - xylem), 7 - accessory bundle, 8 - medullary ray, 9 - pith.

6. Anatomical structure of stems in woody angiosperms and gymnosperms

Fig. 8. Stems of woody angiosperms:

A - Betula verrucosa Ehrn.; B - Tilia cordata Mill.: 1 - at low magnification, 2 - at high magnification: 1 - periderm, 2 - collenchyma, 3 - cortical parenchyma with druses, 4 - parenchyma of the medullary ray apex, 5 - secondary phloem (bast) (a - bast fibers, b - sclereids (thick-walled bast), c - sieve tubes with companion Cells and bast parenchyma (thin-walled bast)), 6 - cambium, 7 - secondary xylem (wood) (d - early wood elements, e - late wood elements (d, e - annual ring)), 8 - medullary ray, 9 - primary xylem, 10 - pith.

Hard bast is most commonly formed by bast fibers and sclereids, whereas soft bast consists of sieve tubes with companion cells and parenchyma. The annual rings of wood are composed of late wood elements—fiber tracheids and libriform fibers—and early wood tracheal elements, including vessels, pitted tracheids, and wood parenchyma. Based on their histological composition and vessel arrangement, woods can be classified as rayless, ring-porous, or diffuse-porous. In woody plants, the initial layer of the cambium consists of two Cell types: fusiform cells with tapered ends and ray cells that form the parenchyma of the medullary rays. Consequently, cambial derivatives—elements of the secondary stem structure—differ in structure and orientation relative to the longitudinal axis of the organ. Fusiform initials give rise to prosenchymatous elements, while ray initials give rise to radial ones.

Fig. 9. Stem of a gymnosperm plant — Pinus sylvestris L.:

1 - periderm, 2 - cortical parenchyma, 3 - resin duct, 4 - secondary phloem (bast), 5 - cambium, 6 - secondary xylem (wood) (a - early tracheids, b - late tracheids (a, b - annual ring)), 7 - medullary ray, 8 - primary xylem, 9 - pith

Gymnosperm wood consists exclusively of tracheids, whereas the wood of gnetophytes (ephedras) contains vessels. Mechanical tissues in the bark are absent or poorly developed; the phloem comprises sieve cells or sieve tubes lacking companion cells, parenchyma, and occasionally bast fibers or sclereids. Annual rings consist of wide-lumen early tracheids with bordered pits, which perform a conducting function, and narrow-lumen fibrous late tracheids lacking bordered pits, which serve a mechanical support function. All parts of the stem in most conifers are permeated with schizogenous resin ducts.

7. Anatomical structure of rhizomes

A rhizome (rhizoma) is a more or less long-lived, thickened or unthickened shoot bearing adventitious roots, apical and lateral buds, and scale-like leaves or lacking them. Rhizomes are typical of most perennial herbaceous plants, certain shrubs (such as spindle tree), and dwarf shrubs (such as bilberry). Branching of the rhizome leads to The formation of a cluster of aerial shoots originating from a single individual (e.g., lily of the valley, couch grass).

Rhizomes are characterized by the following features:

- storage parenchyma is the most prominent tissue throughout all parts of the organ;

- conducting tissues are poorly developed;

- mechanical tissues are virtually absent;

- chlorenchyma is lacking;

- endogenous secretory structures that accumulate BIOLOGICALLY ACTIVE SUBSTANCES are well developed.

Rhizomes of monocotyledonous plants exhibit a primary polystelic or scattered bundle structure. The protective tissue is a persistent, sometimes lignified epidermis lacking Stomata, trichomes, and cuticle. The primary cortex is well developed, represented by a multi-layered storage parenchyma and a multi-seriate endodermis with U-shaped thickenings of The Cell walls. The central cylinder contains collateral closed or concentric leptocentric (amphicribral) vascular bundles arranged more or less randomly. The pith is weakly defined or hollow.

Fig. 10. Rhizome of a monocotyledonous plant, Convallaria majalis L.:

A - at low magnification, B - at high magnification: 1 - epidermis, 2 - cortical storage parenchyma, 3 - endodermis with U-shaped thickenings, 4 - closed collateral bundle, 5 - concentric leptocentric bundle (a - phloem, b - xylem), 6 - storage parenchyma of the axial cylinder.

Rhizomes of dicotyledonous plants, similar to their stems, possess a Introduction/11.html">Secondary structure of bundle, transitional, or non-bundle types. They are most frequently covered by a loose periderm; the cortical and medullary parenchymas partially break down by the end of the growing season; the endodermis is starch-storing; and the vascular bundles of the central cylinder are small, open, collateral, or bicollateral. Leaf traces are scattered within the cortical region.

Fig. 11. Rhizome of a dicotyledonous plant of transitional type - Tussilago farfara L.:

A - under low magnification, B - under high magnification: 1 - periderm, 2 - storage parenchyma of the cortex, 3 - lacuna (cavity), 4 - vascular bundle (a - sclerenchyma, b - phloem, c - cambium, d - xylem), 5 - medullary ray, 6 - storage parenchyma of the pith.

Classification of Rhizomes

Summary Table of Rhizome Anatomy

8. General scheme of the histological composition of parts of plant axial organs

9. General scheme of the histological composition of parts of plant axial organs