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,单击此处编辑母版标题样式,*,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,第五章 植物器官的结构及组织分化,四、花,Flower,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 three 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,both 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.,Monocots.(a)A member of the palm,family,ily,the coconut palm(,Cocos,nuci,-,fera,),grozoing,in,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,sativa)is a member of,the grass family.,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(,Carnegiea,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,穗状花序,伞形花序,伞房花序,总状花序,圆锥花序,柔荑花序,复伞形花序,头状花序,肉穗花序,（一）花的组成与基本结构,花,花柄,Pedicel,花托,Receptacle,花被,Perianth,雄蕊群,Androecium,雌蕊群,Gynoecium,1,、花柄和花托,下位花,周位花,上位花,2,、花被,花萼,Calyx,花冠,Corolla,萼片,：由薄壁组织、维管系统及表皮层组成,Sepal,表皮层上有气孔和表皮毛,花瓣,：,由薄壁组织、维管系统及表皮层组成,Petal,表皮层细胞的垂周壁呈波纹状或内脊，,表皮层上有气孔和表皮毛,薄壁组织中可含有一些异细胞，成熟,花瓣中 有有色体或细胞液中有花青素,3,、雄蕊群,花药,Anther,花丝,Filament,4,、雌蕊群,子房,Ovary,花柱,Style,柱头,Stigma,基本单位是心皮,Carpel,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.,(b)A partly,dissected 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 flower,of three,fused,carpels,.Such a flower is said to,be,hypogynous,.,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,ossporopollenin,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 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 grain.(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.,Mature pollen grain of,Lilium,contain-,ing,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 nucleolus.,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,is shed at the three-celled,stage,whereas that of,Lilium,shown,in the preceding figure,is shed at the,two-celled stage.,侧膜胎座,中轴胎座,特立中央胎座,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,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
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