Research Background

Flowering plants have four major part types: roots, stems, leaves and flowers. These parts each have different responsibilities.

Roots are responsible for anchoring the plant to the ground and extracting water and minerals from the soil. There are three types of roots: taproots, fibrous roots and adventitious roots. Taproots are large and fleshy in appearance and grow deep into the ground to search for food. They can also store food, which is particularly necessary for perennial plants during periods of dormancy. Taproots are mostly found in plants with two seed-leaves (dicots). Fibrous roots lie close to the surface of the soil and collect precipitation before it sinks deep into the ground. This type is mostly found in plants with one seed-leaf (monocots). Adventitious roots develop to help the plant climb, for example ivies, and help develop modified underground stems, such as bulbs. They are common in both dicots and monocots.

Stems are responsible for supporting leaves and flowers physically, holding the leaves and flowers in the best position for food gathering and reproduction and storing nutrients for future use. Stems may be simple, branched, upright or creeping and can form underground food storage organ.

Leaves are responsible for absorbing the sun’s rays, the majority of the photosynthetic production, taking in carbon dioxide and releasing oxygen and water vapor (breathing), and removing waste products from the plant. Usually, the largest leaves grow closest to the ground so they don't block the leaves below them from the sun. To maximize the amount of surface area exposed to the sun, leaves are arranged in many different ways: alternate, opposite and whorled. An alternate leaf arrangement involves one leaf per node (point of attachment to the stem). An opposite leaf arrangement involves two leaves per node, while a whorled leaf arrangement involves three or more leaves per node.

Flowers are responsible for one important function: reproduction. There are many different kinds of flowers in the plant kingdom. They are composed of modified shoots and leaves that vary in shape, size, number, etc.

Temperature influences a wide variety of plant functions, so it is not surprising that soil temperature affects root growth in many ways and that expansion of crop root systems in temperate regions is limited by cool soil temperatures. Root system expansion is a function of three temperature dependent processes: growth, development, and orientation. Temperature affects root growth through its influence on root weight, root length, and root diameter. Root development is affected by temperature's effect on root initiation and root turnover. Lastly, temperature controls root orientation through its impact on the direction of root growth and the gravitropic response.

Warm seasons vegetables do best when temperatures average 65 to 95 degrees. They thrive in warm summers and should be planted after the danger of frost is over in the spring. Favorite warm season vegetables include beans, cucumbers, eggplant, peppers, summer squashes and tomatoes.

Plant cool season vegetables several weeks before the last spring frost is expected in your location. They grow best when daily temperatures reach only 55 to 75 degrees. The most popular cool season vegetables are beets, broccoli, cabbage, carrots, green onions, peas, radishes and spinach.

Most science students do not have the opportunity to observe the development of a plant’s root system. They observe stems, leaves, and flower development, but the root system is usually hidden beneath the surface of the soil. Materials and procedures are available that enable a student to make root development observations. This mini-research unit will describe how a teacher can uncover this world down under for his/her students.