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1、1,2,3,The duckweeds (family Lemnaceae) are the smallest flowering plants; their struc- tural features mark them as extremely reduced relatives of the aroid family (Araceae), the family that includes calla lilies (Zantedeschia) and Philodendron. (a) A honeybee resting on a dense float- ing mat of thr
2、ee species of duckweed. The larger plants are Lemna gibba, about 2 to 3 millimeters long; the smaller ones,are two species of Wolffia, up to 1 milli- meter long. (b) A flowering plant of W. borealis, with a circular concave stigma (looking like a tiny doughnut) and a min- ute anther just above it, b
3、oth protruding from a central cavity. The whole plant is less than 1 millimeter long. (c) Flower- ing plant of L. gibba; two stamens and a style protrude from a pocket on the upper surface of the plant.,4,Monocots. (a) A member of the palm family, ily, the coconut palm (Cocos nuci- fera), grozoing i
4、n Tehuantepec, Oaxaca, Mexicon. The fruit of coconut is a drupe, not a nut (see Chapter 19).,(b) Flowers and fruits of the banana plant (Musa X paradisiaca). The banana flower has an in- ferior ovary, and the tip of the fruit bears a large scar left by the fallen flower parts,. (c) Rice (Oryza sativ
5、a) is a member of the grass family.,5,function of the leaves. (c) Round-lobed hepatica (Hepatica americana), which flowers in deciduous woodlands in the early spring. The flowers have no petals but have six to ten sepals and numerous spirally arranged stamens and carpels.,(b) Saguaro cactus (Carnegi
6、ea gigantea). The cacti, of which there are about 2000 species, are almost exclusively a New World family. The thick, fleshy stems, which store water, contain chloroplasts and have taken over the photosynthetic,6,穗状花序,伞形花序,伞房花序,总状花序,圆锥花序,7,柔荑花序,复伞形花序,头状花序,8,9,10,11,肉穗花序,12,13,1、花柄和花托,下位花,周位花,上位花,14,
7、15,16,Parts of a lily (Lilium henryi) flower. (a) An intact flower. In some flowers, such as lilies, the sepals and petals are similar to one another, and the perianth parts may then be referred to as tepals. Note that the sepals are attached to the receptacle below the petals.,17,(b) A partly disse
8、cted flower with two tepals and two stamens removed to reveal the ovary. The gynoecium consists of the ovary, style, and stigma. The stamen consists of the filament and anther. Note that the sepals, petals, and stamens are attached to the receptacle below the ovary, which is made up, in the lily flo
9、wer, of three fused carpels. Such a flower is said to be hypogynous.,18,19,20,21,22,The wall of the pollen grain serves to protect the male gametophyte on its often lIozardous journey between the anther and the stigma. The outer layer, or exine, is composed chiefly of a substance known ossporopollen
10、in, which appears to be a polymer composed chiefly of carotenoids. The exine, which is remarkably tough atld resistant, is often elaborately culptured. The sculpturing of pollen grain walls is very precise and distinctly different from one species to another, as revealed ill these scanning electron
11、micrographs,of pollen grains. (a) Pollen grains of the horse chestnut (Aesculus hippocasta- num). The pore of each grain through which a pollen tube may emerge is vis- ible in the furrow. (b) Pollen grains of a lily (Lilium longiflorum). (c) Detail of the surface of a lily (L. longiflorum) pollen gr
12、ain. (d) Pollen grain of the western ragweed (Ambrosia psilosta- chya). The pollen of ragweed is a primary cause of hay fever. Spiny pollen grains such as these are common among members of the sunflower family, Aste- raceae, of which ragweed is a member.,23,Mature pollen grain of Lilium, contain- in
13、g a two-celled male gametophyte. The spindle-shaped generative cell will divide mitotically, giving rise to two sperm; the larger tube cell, which contains the gen- erative cell, will form the pollen tube. The round structure above the generative cell is the tube cell nucleus, with its red-stained n
14、ucleolus.,24,Mature pollen grains-three-celled male gametophytes of the telegraph plallt, Silphium (family Asteraceae). Prior to pollination, each pollen grain contains two filamentous sperm cells, which are suspended in the cytoplasm of the larger tube cell. In other words, the pollen of Silphium i
15、s shed at the three-celled stage, whereas that of Lilium, shown in the preceding figure, is shed at the two-celled stage.,25,侧膜胎座,中轴胎座,特立中央胎座,26,Lilium. Some stages in development of all ovule and embryo sac. (a) Two young ovules, each with a single, large mega- sporocyte. Integuments have not begun
16、 to develop. (b) Ovule now has integu- ments. The megasporocyte is in the first prophase of meiosis. (c) Ovule with eight-nucleate embryo sac (only six of tile nuclei can be seen here, two at the chalazal end and four at the micropylar end). The polar nuclei have not yet migrated to the center of the sac.,27,28,五、种子 Seed,珠被 受精卵 受精极核,29,30,31,32,33,34,35,36,37,38,39,