Zea mays

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7.26 7.26 Fine rOOfS from a large tree of the dicotyledon Fraxlnus excelsior (ash) growing in the cracks of a rock face. These toon have grown down from the main branch roors in ,he soil above and their expansion by secondary Ihickening growth, helps 10 further break open the exposed rock face. 7.27 7.27 TS of the fleshy root of the dicotyledon Daucus ,;arota (carrot). The narrow core of primary xylem (1) is surrounded by an extensive hut mainly parenchymatous secondary Jlylem (2) in which a few tracheaey elements OCCUt. The welldefined vascular cambium (3) also produces centrifugally a largely parenchymatous secondary phloem (4). Cortex (5). (LM x 30.) 7.28 144 I Primary xylem. 2 Secondary xylem 3 Vascular cambium 4 Secondary phloem 5 Conex 7.28 TS showing detail of the fleshy root of the dicotyledon Bela vulgaris (beetroot). The vascular cambium produces eJltensive patenchyma in the secondary xylem; supernumery cambia (1) arise within this tissue giving rise to discrete sttands of xylem (2) and phloem (3). (L:\1 x 30.) 1 Supcrnumery cambia 2 Xylem strands 3 Phloem strands
CHAPTER 8 Sexual reproduction Introduction The great majority of ferns arc homosporous, with numerous haploid spores being produced by meiosis in the sporangia borne on the leaves of rhe diploid plant (sporophyte, 1.7). When the spores are shed rhey develop into small, but free-living, green gametophytes (8.1) on which the gametes 3rc later formed. Fusion of the motile sperm with the egg results in a diploid embryo; this reestablishes the sporophyte generation which is soon independent of the gamctophyrc. The seed plants are heterosporous and do not show a free-living gamctophyce generation. In the gymnosperms a single haploid megaspore matures to form the embryo sac within the naked female ovule (1.5, 1.32). This megaspore is formed by the meiosis of a solitary meg:lspore mother cell located in the diploid nucellus (megasporangium). Only one of the four resulram spores matures while the others abort (1.32). Both the embryo sac and nuceUus are enclosed within an inregumenr and these strucrures collectively constitute the ovule (1.32) which is retained on the tree (1.5). The haploid megaspore divides repeatedly to form a mass of gametoph}'tic tissue within the enlargened embryo sac, and eventually one or more eggs become demarcated within this tissue close to the micropyle (8.2). Following pollination of the ovule by a microspore, the egg is fertilised by a sperm and the diploid embryo develops. The testa of the marure seed is formed from the modified integument of the ovule, while copious food reserves for the future seedling are contained within the tissue of the female gametophyte surrounding the embryo (1.32,8.2). In flowering plants the ovule is enclosed within an ovary (1.32) in contrast to the exposed ovule in gymnosperms (1.5). The female gamerophyte within the embryo sac is typically reduced to eight cells and one of these, at the micropylar end of the embryo sac. represents the egg (1.32). In contrast to gymnosperms double fertilisation occurs in angiosperms with one sperm fertilising the egg to form the diploid embryo (1.33) while the other sperm fertilises the twO central polar nuclei to form the triploid, nutritive endosperm (1.32) which is initially coenocytjc. General features of flowers Most flowers contain both male and female sex organs (1.1,1.31) but some flowers are unisexual (8.3) and may occur on the same plant (8.3) or separale individuals. The flower of Magnolia (1.31) illustrates the general features of a dicolyledon. The upper half of the elongate receptacle (floral axis) is covered by a large number of spirally arranged and separate female organs (carpels) which collectively constirute rhe apocarpous gynoecium. Below the carpels numerous spirally arranged male organs (stamens constituting the androecium) are inserted ontO rhe receptacle by shorr filaments. These are rerminalcd by large anthcrs containing the pollen (microspores). Ar the base of the receptacle there are usually nine large, petaloid, periamh members. In contrast with Magnolia, the monocotyledonous flower of Lilillm (1.1) has six petaloid periamh members arranged in two alternating whorls. These encircle six stamens, while the syncarpous gynoecium consists of three fused carpels. The three comparnnents of the ovary arc clearly visible on the fcuits developing after the flowers wither (1.1). The ovary in Li/ium is terminated by a long. slender style which is tipped by a slightly swollen stigma. As in Magnolia the ovary is superior since its poinr of insertion lies above Ihe rest of the floral parts, but in orher flowers the ovary may be inferior (8.4). In the early dcvclopmcnl of most flowers the organ primordia arise in centripetal sequence so that the petiamh is iniri
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A Colour Atlas of PLA T STRUCTURE B
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5 The green leaf 97 Introduction 97
Page 7 and 8:
• CHAPTER 1 Introduction The asso
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1.6 1.6 L}'copusicon e$culentum (to
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1.17 1.19 ,--------------::c-=-----
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1.22 1.22 Group of rail Cordy/hIe a
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1.32 B 24 1 6 \ -H-r 14 13 c 11 """
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times becomes highly lobed (2.15, 2
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stack (2.14, 2.52) of smooth cister
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2.14 2.14 Diagram of the fine-struc
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2.39 Longitudinally-sl:crionl:d l:h
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CHAPTER 3 Plant histology Disttibut
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3.1 3.2 3.1 TS of the: petrified st
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3.21 ,-------------, 3.23 3.2J Non-
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3.31 TS of n cortienl mucil:lge duc
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3.41 -+-2 3.39 L$ of the phloem of
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3.58 80 3.56 3.56 TS of tbe seconda
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absent or may develop some distance
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4.2 4.3 r-----;; 4.2 RLS of the ext
Page 91: 4.24 4.24 TS of a vascular bundle f
Page 97 and 98: secretion may temporarily accumulat
Page 99: 5.3 ,--------------, 5.3 Large fan-
Page 112 and 113: 5.45 5.44 IS of the petiole of the
Page 114 and 115: 5.50 116 5.50 Base of the mature tr
Page 116 and 117: fibres often develop in the outer p
Page 120: 6.7 6.7 5hool of the monocotyledon
Page 129 and 130: 6.33 6.32 TS showing distribution o
Page 134: 7.4 I'neumatophores of Alliceimia n
Page 137: 7.14 l.S of a later:J.1 root primor
Page 144 and 145: pappus (calyx, 8.9) of each floret
Page 146: tube frequently corers the embryo s
Page 155 and 156: S.19 TS of imm,lIure pollen sacs in
Page 157: 8.25 8.25 Mature pollen grain of th
Page 169: 8.64 hnmarure fruir of rhe dleot)·
Page 180 and 181: a tetraploid h3.S a double: set. Po
Page 183 and 184: Vacuole An organelle bounded by rhe
Page 185 and 186: Cell (continued) meiosis 158, 161,
Page 188: Sanicula europea (sanicle) 68 Sanse
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Zea mays

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