Botany - B.E. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter III. Vegetative Plant Organs
Laboratory Class Topic 6.12. Root Morphology. Types of Root Systems. Root Metamorphoses

General Remarks. A young plant begins to develop from its ROOT as it transitions to an independent lifestyle. This process gives rise to various types of roots and root systems, as well as their modifications. Roots anchor the plant in the soil, supply it with Water and dissolved minerals, and perform additional Functions. Understanding root Morphology, its modifications, and their properties makes it possible to apply appropriate technological practices when cultivating crops for various purposes.

Objects:

1. Bean seedlings (Phaseolus vulgaris L.)

2. Wheat seedling and root system (Тriticum aestivum L.)

3. Corn root system (Zеа maуs L.)

4. Common lambsquarters root system (Сhеnopodium album L.)

5. Tomato root system (Lycopersicon esculentum Mill.)

6. Beet root crop (Веtа vulgaris L.)

7. Radish root crop (Raphanus sativus L.)

8. Lupine root system (Lupinus polyphillus Lindl.)

9. Carrot root crop (Dаuсus sativus (Ноffm.) Rоеhl.)

10. Dahlia tuberous roots (Dаhlіа ріnnаtа Саv.)

Tasks:

1. Examine and draw the FEATURES OF PLANT seedlings.

2. Examine and draw the root shapes of various plant species.

3. Examine and draw the types of plant root systems.

4. Examine and draw the modifications of plant roots.

Equipment and Materials: stereomicroscopic Microscope, binocular and hand magnifiers, scalpels, forceps, herbarium and fixed material of seedlings, roots, and root systems.

Macroscopic study of a bean seedling. To study dicotyledonous seedlings, fixed or herbarium samples of bean seedlings can be used. Take a bean seedling and place it on a Glass slide. Examine it carefully (Fig. 43). One root stands out as the largest and thickest. This is the primary root, or first-order root, which developed from the embryonic root of the bean seed. Roots branching off from the primary root are called lateral roots, or second-order roots, and those branching from them are third-order roots, and so on. Lateral roots never exceed primary roots in length and thickness.

In the bean seedling, locate the root collar—the transition zone between the root and the stem; it is slightly thicker than the primary root. Above the root collar lies the stem region adjacent to the cotyledons, devoid of any appendages. This is the hypocotyl, or subcotyledonary internode. In young bean seedlings, it is curved. The stem region between the cotyledons and the first pair of true leaves is called the epicotyl, or supercotyledonary internode. Among the true leaves, a tiny bud is visible, whose apical meristem (growing cone) ensures the growth of the bean stem. The region of the stem where leaves attach is called a node, and the segment between two adjacent nodes is an internode.

Macroscopic study of a wheat seedling. For this purpose, seedlings at various Selection/3.html">Stages of development should be used. When examining a young wheat seedling, you will see only the sprouted grain, usually with three rootlets, known as primary roots. Look closely and you will notice that they are arranged unevenly. Among them, identify the central or middle root, which is slightly thicker and emerges lower down—it is considered the primary root (see Fig. 43). Above it and on the sides, two thin rootlets develop, which are called lateral roots.

Seedlings at later stages of development have a more complex Structure. In some of them, find the sprouted grain and the aforementioned primary roots emerging from the lower part. The upper part gives rise to the coleoptile, which covers the embryonic leaves and the stem growing cone.

In seedlings of later developmental phases, locate the tillering node, which is the first node above the sprouted grain. You can easily recognize it as a somewhat thickened stem from the lower part of which adventitious roots emerge, while from the upper part, covered by the leaf sheath, a young SHOOT develops. It should be remembered that adventitious roots are thin and develop only at the tillering nodes. Lateral roots develop from the primary roots.

Draw the various Developmental Stages of wheat seedlings and label their constituent parts.

Macroscopic study of root shapes. Examine and study various root shapes using herbarium specimens, fixed material, and living plants.

Select The Root System of wheat or another cereal plant and examine its roots. They are thin, delicate, long, with root hairs at the tips, visible without a stereoscopic microscope or binocular magnifying glass. These roots belong to the filiform (thread-like) type.

Using a carrot as an example, examine the fusiform (spindle-shaped) root type; its primary root is thickened and somewhat conical, with sparse lateral roots branching off from it.

Examine the napiform (turnip-shaped) root form in radish or garden radish — characterized by a greatly expanded upper part and a sharply tapered lower part, from which lateral roots extend.

Examine the conical root shape in beets or parsley.

Macroscopic study of root systems. In practice, Three types of root systems are distinguished: taproot, fibrous, and mixed.

Take common lambsquarters, lupine, or another dicotyledonous plant from the provided herbarium material and thoroughly study its root system. Pay attention to the fact that among the mass of roots, the primary root (or root of the first order) stands out, giving rise to lateral roots of the second order, which in turn produce lateral roots of the third and subsequent orders. Lateral roots never exceed the size of the primary root. A root system in which the primary root is prominent and accompanied by smaller lateral roots is called a taproot system, or the primary root system (Fig. 44).

Examine the fibrous root system using wheat as an example. Note that in wheat, the primary root is inconspicuous or indistinguishable from the mass of adventitious roots that develop in large numbers from the stem. These adventitious roots are almost all equal in length, thread-like, and form a dense cluster, hence the name — fibrous root system, or adventitious root system.

Examine the Features of the mixed root system in tomatoes, currants, or gooseberries, which combines the characteristics of both fibrous and taproot systems. It features a single prominent primary root and several lateral roots that almost reach the size of the primary root. In this type of root system, you can easily identify a main primary root with lateral roots branching off it, while higher up, originating from the stem, is a system of adventitious roots that are thin, short, and horizontally arranged.

Macroscopic study of root modifications. In connection with performing additional functions, the root undergoes various modifications. Let us examine the main ones.

Root crops. Examine the Structural Features of root crops using sugar beets as an example (Fig. 45).

Take a root crop and study it thoroughly. Its upper part, which bears leaves (buds), forms the crown (HEAD). By origin, this is the stem portion (epicotyl). The middle, thickest part constitutes the neck (collar), formed by THE CONTRIBUTION OF both the epicotyl and hypocotyl. The third, lower part represents the true root. You can easily recognize it because branched lateral roots extend from it on two sides. The root crop is formed As a result of the accumulation of nutrient reserves.

Root tubers, or root tubers. Examine the structural features of root tubers (root tubers) using dahlia or dropwort as an example. Note that it is not the primary root, but the lateral roots that become thickened and transform into root tubers. Adventitious buds are visible on the root tubers, through which these plants propagate.

Prop roots. Inspect and study the prop roots in corn. Pay special attention to the lower part of the stem, to the first internodes, where specific prop roots emerge upon contact with moist soil. These are quite strong and long roots arranged in a ring around the stem. By origin, they are adventitious roots that perform mechanical support and respiratory functions.

Examine root nodules in lupine (Fig. 45).

It is easy to notice that its root system is of the taproot type. Numerous swellings — root nodules — are visible on the primary and lateral roots as a result of Symbiosis between nitrogen-fixing Bacteria and the plant. If they are sectioned and examined under a microscope, it is evident that the main part of the nodule consists of the fundamental parenchyma (bacteroidal tissue), surrounded by the epiblema with root hairs.

Conclusions. 1. Depending on origin, habitat conditions, and the performance of primary physiological functions, plants have developed A wide variety of roots and root systems.

2. As a result of performing additional functions, the MORPHOLOGY AND ANATOMY of roots have undergone alterations, leading to The formation of various modifications.

Self-control questions

1. Which root is referred to as the primary root?

2. What is THE ORIGIN OF adventitious and lateral roots?

3. Define a root system.

4. Characterize the taproot system.

5. List the distinguishing features of taproot and fibrous root systems.

6. Name the primary root modifications.

7. What is the origin of root tubers, and what function do they perform?