Botany Basics ❂1

Botany Basics ❂1 lants are unique and essential to life on earth. Unlike most living things, plants make their own food from ❂ TOPICS IN THIS CHAPTER P sunlight and water. Either directly or indirectly, they are the primary food source for humans and other animals. ❂ Plant life cycles Additionally, they provide fuel, replenish the earth’s oxygen ❂ supply, prevent soil erosion, slow down wind movement, Internal plant parts cool the atmosphere, provide wildlife habitat, supply me- ❂ External plant parts dicinal compounds and beautify our surroundings. ❂ Plant growth and development Many plants are familiar to us, and we can identify and ❂ Environmental factors appreciate them based on their external structures. How- affecting growth ever, their internal structures and functions often are over- ❂ Plants in communities looked. Understanding how plants grow and develop helps ❂ Plant hormones and growth us capitalize on their usefulness and make them part of our regulators everyday lives. This chapter focuses on vascular plants. Vascular plants contain xylem and phloem, which are the water, nutrient and food conducting tissues. Ferns and seed-producing By Ann Marie VanDerZanden, Extension Master plants fall into this category. We will distinguish between Gardener State Coordinator, Oregon State monocotyledonous and dicotyledonous plants. Sometimes University. called monocots and dicots for short, these plants have im- Adapted by Jay Moore, former Land Resources portant distinguishing characteristics. For example, mono- Agent, Cooperative Extension Service, University cots (e.g., grasses) produce only one seed leaf (cotyledon) of Alaska Fairbanks. Table 1.—Comparison between monocots and dicots. Structure Monocots Dicots Seed leaves One Two (cotyledons) Vascular system Xylem and phloem are paired in bundles, Xylem and phloem form rings inside the stem. which are dispersed throughout the stem. The phloem forms an outer ring, the xylem an inner ring. Floral parts Usually in threes or multiples of three. Usually in multiples of four or five. Leaves Often parallel-veined. Generally net-veined. 4 • Botany Basics—Chapter 1 Botany terminology Ovary—The part of a female flower where Anther—The pollen sac on a male flower. eggs are located. Apex—The tip of a shoot or root. Petiole—The stalk that attaches a leaf to a Apical dominance—The tendency of an api- stem. cal bud to produce hormones that suppress Phloem—Photosynthate-conducting tissue. growth of buds below it on the stem. Photosynthate—A food product (sugar or Axil—The location where a leaf joins a stem. starch) created through photosynthesis. Cambium—A layer of growing tissue that Photosynthesis—The process in green plants separates the xylem and phloem and con- of converting carbon dioxide and water tinuously produces new xylem and phloem into food (sugars and starches) using en- cells. ergy from sunlight. Chlorophyll—The green pigment in leaves Pistil—The female flower part; consists of a that is responsible for trapping light energy stigma, style, and ovary. from the sun. Respiration—The process of converting sug- Chloroplast—A specialized component of ars and starches into energy. certain cells; contains chlorophyll and is Stamen—The male flower part; consists of an responsible for photosynthesis. anther and a supporting filament. Cortex—Cells that make up the primary tis- Stigma—The top of a female flower part; col- sue of the root and stem. lects pollen. Cotyledon—The first leaf that appears on a Stoma (pl. stomates, stomata)—Tiny open- seedling. Also called a seed leaf. ings in the epidermis that allow water, Cuticle—A relatively impermeable surface oxygen and carbon dioxide to pass into layer on the epidermis of leaves and fruits. and out of a plant. Dicot—Having two seed leaves. Style—The part of the female flower that Epidermis—The outermost layer of plant connects the stigma to the ovary. Pollen cells. travels down the style to reach the ovary, Guard cell—Epidermal cells that open and where fertilization occurs. close to let water, oxygen and carbon diox- Transpiration—The process of losing water ide pass through the stomata. (in the form of vapor) through stomata. Internode—The space between nodes on a Turgor—Cellular water pressure; responsible stem. for keeping cells firm. Meristem—Specialized groups of cells that Vascular tissue—Water-, nutrient- and pho- are a plant’s growing points. tosynthate-conducting tissue (xylem and Mesophyll—A leaf’s inner tissue, located phloem). between the upper and lower epidermis; Xylem—Water- and nutrient-conducting contains the chloroplasts and other special- tissue. ized cellular parts (organelles). Monocot—Having one seed leaf. Node—An area on a stem where a leaf, stem or flower bud is located. Chapter 1—Botany Basics • 5 while dicots (broadleaf plants) have lengths. This is one reason why spin- two. The vascular systems, flow- ach, radish and beets can be hard ers and leaves of the two types crops to grow in Alaska. These of plants also differ (Table 1). plants bolt instead of produc- These differences will be im- ing a good crop of leaves portant in our discussion of or roots. This situation can plant growth and develop- also occur when plants are ment. exposed to extreme environmental conditions such as temperature variation and Plant life cycles drought. A plant is classified as either an Perennial plants live more than 2 annual, biennial or perennial based on years and are grouped into two categories: its life cycle or how many years it takes herbaceous perennials and woody perennials. to produce flowers and seeds. Herbaceous perennials have soft, non- An annual, such as a marigold, completes woody stems that generally die back to the its life cycle in 1 year. Annuals go from ground each winter. New stems grow from seed to seed in 1 year or growing season. the plant’s crown each spring. A delphinium During this period, they germinate, grow, is an example of an herbaceous plant. Trees mature, bloom, produce seeds and die. and shrubs, on the other hand, have woody Summer annuals complete their life cycle stems that withstand cold winter tempera- during spring and summer; most winter an- tures. They are referred to as woody peren- nuals complete their growing season during nials. fall and winter. There are both winter and summer annual weeds, and understanding a weed’s life cycle is important in controlling Internal plant parts it. Of course, in most locations in Alaska Cells are the basic structural and physi- the temperature does not allow for winter ological units of plants. Most plant reac- See Chapter 4, annuals. Some plants that are winter annu- tions (cell division, photosynthesis, respira- Plant Propagation. als in warmer climates act as summer annu- tion, etc.) occur at the cellular level. Plant als in Alaska. tissues are organized groups of similar cells A biennial completes its life cycle in 2 that work together to perform a specific years. During the first season, it produces function. An example would be the xylem, vegetative structures (leaves) and food stor- which functions to move the water through age organs. The plant overwinters and then a plant or the phloem that moves food. produces flowers, fruit and seeds during its Plant cells are totipotent. In other words, second season. Swiss chard, carrots, beets, plant cells retain all of the genetic informa- sweet William and parsley are examples of tion (encoded in DNA) necessary to devel- biennials. op into a complete plant. This characteristic Biennials can sometimes go from seed is the reason vegetative (asexual) reproduc- germination to seed production in one grow- tion works. It is why it is so easy to share ing season. This phenomenon is referred houseplants with friends. For example, the to as bolting. It is a common occurrence in cells of a small leaf cutting from an African Alaska due to the midnight sun, or long day violet have the genetic information neces- 6 • Botany Basics—Chapter 1 sary to generate a root system, stems, leaves Leaf primordia and ultimately flowers. This characteristic Shoot apex also allow growers to utilize tissue culture to propagate disease-free potatoes, orchids, etc. Specialized groups of cells or tissue Leaf called meristems/meristematic tissues are a plant’s growing points. Meristems are the site of rapid, almost continuous cell divi- Bud sion. These cells either continue to divide or differentiate into tissues and organs. How they divide is controlled by a complex ar- ray of plant hormones and environmental conditions. Meristems can be manipulated Stem to change plant growth patterns, flowering, branching or vegetative growth. Vascular tissue External plant parts Soil line External plant structures such as leaves, stems, roots, flowers, fruits and seeds are Lateral root known as plant organs. Each organ is an or- Primary ganized group of tissues that work together root to perform a specific function. These structures can be divided into two groups: sexual reproductive and vegetative. Sexual reproductive parts produce seed; they include flower buds, flowers, fruit and seeds. Veg- etative parts (Figure 1) include roots, stems, Figure 1.—Principal parts of a vascular plant. shoots, nodes, buds and leaves; they are not directly involved in sexual reproduction. Roots typically originate from the lower Vegetative parts often are used in asexual portion of a plant or cutting. They have forms of reproduction such as cuttings, bud- a root cap, but lack nodes and never bear ding or grafting. leaves or flowers directly. Their principal functions are to absorb nutrients and mois- Roots ture, anchor the plant in the soil, support the Often roots are overlooked, probably stem and store food. In some plants, roots because they are less visible than the rest of can be used for propagation. the plant. However, it’s important to under- Structure stand plant root systems because they have a pronounced effect on a plant’s size and Internally, there are three major parts of a vigor, method of propagation, adaptation to root (Figure 2): y soil types and response to cultural practices The meristematic zone is at the tip and and irrigation.

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