BOTANY: LABORATORY PRACTICUM (PLANT ANATOMY AND MORPHOLOGY) — O.A. SHEVCHUK — 2014

THE FLOWER

Background Information. Flowering plants (angiosperms) represent the most diverse division of the plant kingdom, comprising over 240,000 species that inhabit all climatic zones and A wide variety of ecological niches. They form the fundamental plant biomass of the biosphere and constitute the most vital group of plants for humanity. Emerging during the Cretaceous period of the Mesozoic era, flowering plants rapidly spread and assumed a dominant position on the planet.

An essential characteristic of angiosperms is the flower, which develops from a bud and represents a shortened SHOOT performing a reproductive function. A typical flower consists of a pedicel, receptacle, perianth, gynoecium, and androecium.

The pedicel is the stalk that connects the flower to the shoot. Flowers lacking a pedicel are termed sessile. The receptacle is the expanded upper portion of the pedicel to which the other floral Organs are typically attached; its shape varies greatly. A convex or sometimes elongated receptacle, a spiral arrangement of floral parts upon it, and an indefinite number of these parts are considered primitive floral traits. Conversely, a flat or concave receptacle and a definite number of floral elements are characteristic of more highly evolved angiosperms.

The perianth is the floral envelope that performs a protective function and serves to attract insect pollinators. A simple perianth consists solely of a calyx, as in herb-paris (Paris quadrifolia), or a corolla (usually brightly colored), as in the tulip. A double perianth consists of both a calyx and a corolla (e.g., in the cherry). The calyx is composed of green sepals, which may be distinct (polysepalous) or fused (gamosepalous), while the corolla may likewise consist of separate or fused petals. Petals vary greatly in shape and color. In a polypetalous corolla (such as in cherry or cabbage), the petals fall off individually. A gamopetalous corolla may be tubular, ligulate, pseudoligulate, funnel-shaped, rotate, or bilabiate. In some plants, the perianth is reduced to scales or entirely absent, in which case the flower is termed naked. A corolla or flower through which more than one plane of Symmetry can be passed is called regular, or actinomorphic, whereas a flower through which only a single plane of symmetry can be passed is called irregular, or zygomorphic.

The most crucial reproductive elements of the flower are the gynoecium and the androecium. The gynoecium is the aggregate of carpels that form one or more pistils. If a pistil is formed by a single carpel or several unfused carpels, the gynoecium is termed apocarpous. A pistil consisting of fused carpels forms a syncarpous gynoecium, which can be unilocular or multilocular. A pistil typically consists of an Ovary, style, and stigma. Inside the ovary are ovules, within each of which the female gametophyte (the eight-nucleate embryo sac) develops from a single megaspore.

The androecium is the aggregate of stamens. A stamen consists of a filament, an anther, and a connective. Microspores are formed within the anthers and develop into highly reduced male gametophytes (bicellular pollen grains).

An exceptionally important distinguishing feature of flowering plants is double Fertilization, which results in The formation of both an embryo and a secondary endosperm. While in gymnosperms the endosperm develops prior to fertilization and Functions as the female gametophyte, in angiosperms it is triploid and incorporates both maternal and paternal genetic contributions. This circumstance allows double fertilization to be viewed as an advanced evolutionary adaptation that enhances the vigor of the progeny as well as their morphological and ecological plasticity. In angiosperms, as in the vast majority of vascular plants, The life cycle involves the alternation of two generations—the sporophyte and the gametophyte—with the sporophyte being dominant. There is an even greater reduction of the gametophytes compared to gymnosperms, along with their accelerated development driven by a minimal number of mitotic divisions. The gametophytes of flowering plants have lost archegonia and antheridia entirely.

TOPIC 5. FLOWER MORPHOLOGY. THE PERIANTH

General Remarks. The flower is one of the most defining features of angiosperm plants, hence their common designation as flowering plants. The flower is a generative organ that evolved as a metamorphosed, shortened, and unbranched shoot adapted for the formation of micro- and megaspores and Gametes, the execution of Pollination and Fertilization, and the subsequent production of fruits and seeds. The most vital part of the flower is the pistil, particularly the ovary, wherein ovules originate and subsequently transform into seeds.

Objective: to examine The Structure of the flower, The Diversity of flowers in nature, and the Main Trends in their evolution, as well as to acquire practical skills in the morphological analysis of flowers from various plants.

Materials and Equipment: living or fixed flowers of Martagon lily (Lilium martagon), wild radish (Raphanus raphanistrum) or wild cabbage (Brassica oleracea), creeping buttercup (Ranunculus acer), apple (Malus domestica) or sour cherry (Cerasus vulgaris); garden pea (Pisum sativum) or common bean (Phaseolus vulgaris), potato (Solanum tuberosum), chicory (Cichorium intybus), larkspur (Consolida regalis), common sage (Salvia officinalis), cereal rye (Secale cereale), along with Laboratory glassware, microscopes, botanical charts, and anatomical models.

Tasks

1. Examine the general STRUCTURE OF THE actinomorphic cherry flower.

2. Study the Structural Features of the papilionaceous pea flower.

3. Examine the structure of the zygomorphic, bilabiate flower of common sage.

4. Study the structure of the spikelet and flower of rye.

Label the drawings and formulate your Conclusions.

Conclusion

Self-Check Questions

1. WHAT IS A flower and what parts does it consist of?

2. Describe the components of a flower and indicate their functions.

3. What parts make up the perianth?

4. What is the Biological Role of the perianth?

5. What is a flower with radial symmetry called?

6. What are flowers without a perianth called? Give Examples.

7. Name the component parts that form the corolla of a pea flower.

8. What is a flower called through which theoretically only one plane of symmetry can be drawn?