Biology 3B Lab Flowers & Fruits Page 1 of 9 Biology 3B Flowers and Fruits Objectives • To understand the structure and function of a typical flower • To relate floral structure/function and its importance in angiosperm lifecycle • To understand early embryonic development in a monocot and eudicot • To understand dispersal mechanisms utilized by angiosperms • Examine various types of fruit Introduction In angiosperms, the flower bears the sporophyll which has limited growth duration which ultimate produces the seed. Angiosperm flowers may be a solitary flower or clustered into floral aggregations called inflorescences. In either case, the stalk or peduncle supports the entire flower. In an inflorescence, a pedicel supports the individual flower. The receptacle is the actual portion above the peduncle in which the flower parts attach. As you recall, the structure of a flower is composed of four whorls: calyx, corolla, stamen and carpel. The first two whorls are sterile and attached to the receptacle. The collection of sepals form the calyx which often times resemble thick green leaves. The collection of petals form the corolla. Unlike the sepals, the petals are often brightly colored and thinner. However, in some species, the petals resemble the sepals in color and texture. Together, the calyx and corolla form the perianth. The stamens and the carpels form the fertile part of the flower. The stamens are microsporophylls consisting of anther and filament. The filament is the stalk structure that supports the anther. Most anthers are bi-lobed containing four pollen sacs in pairs. Collectively the reproductive male parts are called the androecium or “house of man.” The carpels (or pistil) are megasporophylls consisting of the stigma, style and ovary. Collectively, the female reproductive parts are called the gynoecium or “house of woman.” The stigma is the upper portion of the carpel and produces a sticky substance in which the pollen grains adhere. The pollen tube that develops grows down through the narrow style (absent in some flowers) towards the ovary containing the ovule(s) in the lower part of the carpel. Some flowers contain only a single carpel while other plants may have multiple carpels that are fused. With flowers that have fused carpels, there may be a single style or each carpel may have its own style. In either case, carpels that are fused typically form chambers within the ovary called locules. The number of locules is often related to the number of carpels. Most flowers have both male and female reproductive parts on the same flower. These are called perfect flowers and are monoecious (“single house”). Imperfect flowers have either the male or female reproductive part is absent from the flower. These flowers are dioecious (“two houses”). Imperfect flowers are either staminate (male) or carpellate/pistillate (female). To add more confusion to floral names, flowers that have all four whorls are called complete flowers. Incomplete flowers are those that lack one or more of the four whorls. Thus imperfect flowers are also incomplete. However, not all incomplete flowers are imperfect. The insertion points for the perianth and stamens vary in relation to the ovary or ovaries. If the perianth and stamens insert on the receptacle beneath the ovary, the insertion point is termed hypogynous. In this case, the ovary is said to be superior. If the perianth and stamens insert onBiology 3B Lab Flowers & Fruits Page 2 of 9 top of the ovary, the insertion point is termed epigynous. The ovary is said to be inferior. When the petals and the stamens adnate to the top of the calyx, they form a hypanthium or short tube that arises from the base of the ovary. This type of insertion is called perigynous. ¾ Review your basic floral whorls. Identify the following on a flower: peduncle, pedicel if it is an inflorescence and receptacle. Here’s a webpage that can assist you in learning the basic floral whorls and components: http://www.botany.uwc.ac.za/ecotree/flowers/flowerparts.htm#top TYPES OF INFLORESCENCE Observe the various flowers in the laboratory and be able to identify the following: ¾ Spike: the main axis is unbranched and elongated with sessile flowers are directly attached ¾ Raceme: main axis is unbranched and elongated with flowers attached via a pedicel ¾ Panicle: main axis is branched with the branches bearing flower clusters ¾ Corymb: an inflorescence appearing to have a flat top; indeterminate inflorescence with outer flowers opening first; all flowers typically attached via pedicelBiology 3B Lab Flowers & Fruits Page 3 of 9 ¾ Simple umbel: indeterminate inflorescence, usually but not necessarily flat topped with the pedicels arising form a common point (resembles the stays of an umbrella) ¾ Compound umbel: indeterminate inflorescence, usually but not necessarily flat topped with the peduncles and pedicels arising form a common point ¾ Head: a cluster or ray and disk flowers on a very short axis, peduncle can either be flat or round ¾ Catkin: a spike-like inflorescence with either staminate or carpellate flowers, typically found in woody species ¾ Examine the various flowers in the lab and fill in the following chart: Name Perfection CompletenessOvary position Inflorescence Monoecious/DioeciousBiology 3B Lab Flowers & Fruits Page 4 of 9 FRUITS The ovary evolved through the modification of leaf material resulting in protection and facilitating dispersal of seeds. The ovules develop from the placenta and are attached to the ovary walls until maturation. The arrangement of the placenta is called placentation. If the ovules are on the outer ovary wall or extensions of it the placentation is termed parietal. Axile placentation occurs in flowers where there are several partitions forming locules within the ovary along a central column. Flowers with free central placentation have ovules that are along a central column, however there are no partitions. A flower with a single ovule that develops at either the base or apex of the ovary has either a basal or apical placentation. After pollination, the pollen tube develops and travels down the style to the ovule(s). In angiosperms, there is a