6th grade. Biology. Shoots and buds

Teacher's comments

Leaf arrangement

Regular (spiral) leaf arrangement (see Fig. 4) is an arrangement in which the leaves grow one at a node and are arranged on the stem alternately in a spiral (birch, willow). The leaves minimally shade each other.

Rice. 4. Another location at the bird cherry tree

Opposite leaf arrangement - 2 leaves emerge from one node, located opposite each other (lilac, cloves, mint).

Whorled leaf arrangement (see Fig. 5) - 3 or more leaves emerge from one node (crow's eye, elodea).

Rice. 5. Whorled leaf arrangement of bedstraw

Kidneys

When a seed germinates, the first shoot develops from the bud of the seed embryo. Perennial plants in temperate climates develop new shoots from their buds every year.

The apical bud (see Fig. 6) is a bud located at the top of the shoot.

Rice. 6. Apical bud

An axillary bud (see Fig. 7) is a bud located in the axil of the leaf. Their arrangement follows the arrangement of leaves on the stem.

Rice. 7. Axillary bud

Adventitious bud (see Fig. - a bud developing on an internode on a leaf.

Rice. 8. Accessory bud

Poplar and birch have an alternate arrangement of buds. In lilac, honeysuckle, fuchsia, and elderberry, the buds are located opposite.

After the leaves fall, leaf scars remain on the shoots (see Fig. 9), above which axillary buds are located.

Rice. 9. Leaf scar (highlighted in red)

Escape and bud

The above-ground part of the plant is a shoot or shoot system. A shoot consists of a stem (shoot axis) and leaves and buds located on it. The place on the stem from which a leaf emerges is called a node. The areas of the stem between adjacent nodes are internodes. The angle between the leaf and the stem is called the leaf axil. There are elongated and shortened shoots. Elongated shoots have well-defined internodes. On shortened ones, the nodes are close together and the internodes are very short. Only on them do flowers form and fruits form. Usually the shoot ends with an apical bud. Below the stem, in the axils of the leaves, are axillary, or lateral, buds.

Bud

A bud is an embryonic shoot. The buds vary in appearance (shape, color, size, pubescence) and internal structure.

Based on their internal structure, buds are distinguished between vegetative and generative (floral).

A vegetative bud consists of a shortened stem and rudimentary leaves located on it. The leaves are folded lengthwise or rolled into a tube. Sometimes tiny rudimentary axillary buds can be found in the leaf axils . Inside the bud at the top of the stem there is a growth cone. Thanks to the division, growth and change of its cells, the stem grows, new leaves and buds are formed.

In the generative (floral) buds on the stem, in addition to the rudimentary leaves, there are the rudiments of flowers or one flower. This is clearly visible in elderberry, chestnut, and lilac. The generative buds of many woody plants differ from the vegetative ones in size and shape: they are larger and often rounded.

The buds of trees and shrubs are covered on the outside with dense, leathery bud scales.

Shoot development

In spring, the buds of trees and shrubs swell and increase in size. The bud scales move apart and the tips of green leaves appear between them. This occurs due to the increased growth of internodes.

In the bud, the leaves are located close to each other, as a result, many nodes are formed on the rudimentary stem, so the internodes are very short.

As the buds unfold, the stem cells begin to rapidly divide and grow between the nodes. At the same time, leaf growth occurs. A shoot that develops from a bud during the summer is called an annual shoot.

However, every spring, not all the buds laid in the previous year bloom on trees and shrubs. Usually only the largest, upper buds bloom and form shoots, while the lower, axillary buds remain dormant. Such buds are called dormant.

When the apical bud disappears (due to freezing, biting, pruning), the dormant buds begin to grow and grow into elongated shoots.

Leaf arrangement

The next thing is that the leaves are arranged one at a time (in line) in each node (birch, apple tree, rose, tradescantia, cissus, pelargonium).

Opposite - the leaves are arranged two at each node - crosswise in pairs (lilac, jasmine, mint, jasmine, fuchsia).

Whorled - leaves are arranged in three or more on each stem node - whorl (elodea, raven's eye, oleander, juniper).

Kidney structure

A bud is a rudimentary shoot. The structure of the kidney depends on its type.

The structure of the buds and their location on the stem

Take several shoots of trees or shrubs. Consider them. Determine the location of the kidneys. Sketch it.

Separate several buds from the stem. Consider their external structure. What adaptations help wintering buds withstand unfavorable conditions?

Cut the vegetative bud lengthwise and examine it under a magnifying glass. Using the drawing (see Fig. 10), find the bud scales, rudimentary stem, rudimentary leaves, and growth cone.

Rice. 10. Internal structure of the kidney

Draw a cross-section of a vegetative bud and label the names of its parts.

Study the shape and internal structure of the generative bud. How does its structure differ from the structure of a vegetative bud?

Compare the structure of the bud and the shoot as a whole.

Bud scales are transformed outer leaves. The scales are often impregnated with resinous substances. This protects the kidneys from the penetration of fungi, drying out, and temperature fluctuations.

At the top of the embryonic stem there is a growth cone consisting of meristem cells. On the stems there are rudimentary leaves, in the axils of which there are rudimentary buds.

Shoot development

Germination of wintering shoots of trees and shrubs. In winter, take 2 shoots of a bush or tree. Place 1 shoot in water and the other in a 3% sugar solution. Watch the buds open and shoots develop. Record the results: note the time when the bud scales fall off, the leaves bloom, and the death of the plant.

Vegetative buds are buds bearing only rudimentary leaves. Vegetative shoots sprout from them.

Generative buds are buds that do not have rudimentary shoots with buds at the end. Larger than vegetative ones, differ from them in shape.

Practical work “Escape. The structure of vegetative and generative buds"

Practical work No. 5
“
Escape. The structure of vegetative and generative buds.”

Goal of the work:

Study the morphology of shoots, their underground and above-ground modifications, consider the diversity of buds.

Equipment and materials:

live and herbarium samples of chestnut, hawthorn, ruscus shoots, herbaceous plants, rhizomes, onion bulbs, potato tubers, hairpin, thread, scalpel.

General Information : Stem

– an important axial vegetative organ of the plant. It morphologically and functionally connects the organs of soil (root) and air (leaf) nutrition. Along it there is an upward flow of water and mineral salts from the roots to the leaves and a downward flow of plastic substances from the leaves to places of consumption and their storage for future use. The stem has apical growth, negative geotropism, radial symmetry, and a complex internal structure due to the performance of various physiological functions. It is capable of creating and bearing leaves, branches, flowers, fruits, accumulating reserve nutrients, laying buds, regenerating, and being an organ of reproduction.

The stem with leaves and buds placed on it is called a shoot.

(Fig. 18.) The place on the stem to which the leaf is attached is called
a node
, and the area between adjacent nodes is called
internodes.
Based on the development of internodes, three types of shoots are distinguished:
shortened
(apple tree),
normal
(hazel),
elongated
(ailanthus).
The distance (angle) between the stem and the leaf stalk that extends from it is called leaf axil
.

Fig. 18.

Escape structure

The stem ends at the apex, which is a shortened embryonic shoot.

In the axils of the leaves,
the axillaries
, or

lateral buds

(single, serial, collateral).
Buds that form on internodes, roots, leaves are called accessory
.
In addition to the noted buds, there are also floral
, or
generative
, buds containing only the rudiment of an inflorescence (cherry) or a single flower.
A vegetative
bud consists of a stem growth cone, leaf primordia, bud primordia and bud scales.
in the vegetative-generative
buds, and the growth cone is transformed into a rudimentary flower or inflorescence.
Buds that do not germinate for a long time, but develop only under certain conditions (pruning, freezing), are called dormant.

Fig. 19.

Types of buds: 1 – vegetative, 2 – vegetative-generative, 3 – generative.

The placement of leaves on the stem is: alternate

or
spiral
(apple tree),
opposite
(carnation, lilac) - on one node the leaves are placed on opposite sides of the stem,
whorled
(bedstraw) - three or more leaves come from one node.

Fig.20.

Types of leaf arrangement: a – alternate, b – opposite, c – whorled.

Progress of practical work.

Instruction card.

Macroscopic study of shoot morphology.

Exercise:

Among the herbarium and living material, find shoots of edible chestnut or other species of this genus. Choose typical ones and study them carefully. To do this, it is recommended to use a manual or binocular magnifying glass. It is easy to establish that the shoot consists of a stem as the main supporting part, leaves, buds, nodes and internodes. Take the stem and examine it carefully. Using a scalpel, make a cross section and make sure that the main part of the stem is wood, and the bark and pith occupy a small part of it.

Find living shoots on the stem and show in the picture the nodes - the place of attachment of leaves and internodes between two adjacent nodes. Leaf scars are clearly visible on the stem, left after the leaves fell. Note that these obtuse-shaped scars show leaf marks in the form of bordered punctate formations. In addition, in two-year-old shoots, densely elongated lentils are clearly visible on the stem.

Fig.21.

Horse chestnut shoot: 1 – apical bud; 2 – place of attachment of renal scales; 3 – internodes; 4 – leaf scar; 5 – leaf trace; 6 – lentils.

The leaves of the chestnut tree are placed oppositely. Lateral or axillary buds develop in their sinuses. The shoot ends with an apical bud. Dissect it and study it. You see that externally it is covered with tightly closed brownish covering scales, impregnated along the edges with a sticky resinous substance. Using tweezers, move away the covering scales and underneath them you will see embryonic, green leaves. If you remove them, a lightish growth cone will be revealed, which is the apical educational tissue.

Draw a diagram of the structure of a horse chestnut shoot and label all its parts mentioned.

Macroscopic examination of shoot types according to growth direction.

Exercise:

In the composition of living material and herbarium specimens, select the following types of shoots according to the direction of growth: erect, ascending, creeping, tenacious, curly.

the erect ones first.

shoots. For this, use white quinoa. Its stem is erect, slightly ribbed and woody when mature. Nodes and internodes are clearly visible on it. The leaves are placed alternately, in the axils of many of them lateral shoots are formed, but their sizes are always smaller than the size of the main axis.

Using yellow alfalfa as an example, consider and study the structure of the ascending

escape. Their characteristic feature is their curvature: the lower part of the stem is on the surface of the earth, but does not take root, and the upper part rises and acquires a vertical position in space.

Using creeping clover as an example, familiarize yourself with the structure of creeping clovers

shoots. Their peculiarity is the presence of additional roots that extend from the nodes upon contact with wet soil. Erect stems and inflorescences on long stalks extend from the creeping stem. On these stems, find the apical buds, thanks to which

they lengthen. In creeping strawberry stems, shoots with short internodes are called lashes

, and shoots with elongated internodes -
tendrils
, or stolons.

Using the example of the tenacious bedstraw, familiarize yourself with the clinging

shoots.
Appendages grow along its stems in the form of trailers and hooks. Among the handouts, find woody and herbaceous vines. You can easily recognize them by their well-defined, thin, elongated stems that twine or cling to other plants. Please note that the grape nodes have well-twisted woody tendrils and elongated internodes. Birch has climbing
with normal internodes, while tenacious bedstraw has elongated stems with reverse hooks, with the help of which tenacious and climbing plants are attached to supporting plants.

Fig.22.

Biological types of shoots based on placement in space:

a - erect; b - ascending; c - curly; g - clinging; (c and d - lianas); d – creeping

Macroscopic study of above-ground shoot modifications.

Exercise:

Using the example of hawthorn, familiarize yourself with a modification of the shoot -
the thorn.
Evidence of its shoot origin is

very developed wood. You can see leaves and flowers on the spines

or even fruits.

Tendril

grape is also a modification of the shoot, evidenced by woodiness, its placement in the axil of the leaf.

Using the example of Ruscus, study the structural features of the cladode.

. This

modification of the shoot takes the form of a leaf blade. Please note that it grows from the axil of a modified leaf. In addition, the cladodium, like a typical shoot, bears flowers and fruits, which are formed in the axil of the scaly leaf.

Rice. 23.

Escape modifications:

A - above-ground modifications of the shoot: a - spines; b – cladodes; c – succulent cactus stems; B – underground modifications of the shoot: d – rhizome; d – bulb; e – tuber; 1 – lladodium; 2 – flower; 3 – reduced leaf; 4 – scar (place of leaf attachment); 5 – reduced leaves; 6 – additional roots; 7 – dry integumentary scales; 8 – succulent scales; 9 – kidney; 10 – bottom; 11 – cells; 12 – stolons

Macroscopic examination of underground shoots.

Exercise:

Using the example of a potato tuber, study the structural features of the modified shoot.
Tubers
develop due to the growth of lateral shoots such as stolons.
Nutrients accumulate in them and their structural structure changes. On the surface of the tubers you will recognize eyes
(buds), located in the axils of modified leaves, which look like brow ridges with scaly appendages. If you take a pin and thread and draw it from the top bud to each subsequent one located below, you will find a spiral, alternate arrangement of cells, like leaves or vegetative buds on the stem. When you make a longitudinal section of the tuber, you will see leading elements, just like in the stems.

Draw a potato tuber and label its components.

Fig.24.

Potato tuber.

In wheatgrass, study the structure of the rhizome

, as an example of a modified

escape. It looks like a root, but at the end you will not find a root cap, like

at the root, but an apical bud, which grows the rhizome, like the stem. In addition, leaf scars, internodes, and nodes from which additional roots extend are clearly visible on the rhizome.

Draw a wheatgrass rhizome and label its components.

Fig.25.

Rhizome.

Using the example of an onion bulb, study the structural features of the bulb

.
The latter is an underground modification of the shoot. If you cut it, you will find a short, strong stem - the bottom
with shortened internodes and nodes, from which modified fleshy leaves extend, and from the outside - dry, scale-like leaves. Axillary buds can sometimes be seen in the leaf axils. A bunch of adventitious roots extends from the bottom, as in the stems.

Draw an onion bulb and label its components.

Fig.27.

Bulb.

As conclusions

answer the questions: