5.50 116 5.50 Base of the mature trunk of the palm Corphyra elata. Note the: spiny leaf bases which persiSt for many years after the withered fronds of this monocotyledon have been removed.
CHAPTER 6 The stem Primary growth The aerial stem bears the green photosynthetic leaves and the reproductive organs (1.16,4.13, 6.1, 6.2), while underground stems are frequently perennating and food storage organs (6.3). Most unthickened stems are cylindrical (6.2), but ridged and rectangular forms (6.4, 6.5) 3rc common. Stems are sometimes flattened, leaf-like structures (phylloclades, 6.6, 6.7) with their leaves reduced to scales. The slender xcromorphic stem of Casuarina (6.8) bears only scale leaves, so that phorosynrhesis occurs in the stem cortex which lies adjacent to the longitudinal, hair-lined grooves. [n succulents the stems are swollen and also photosynthetic and in many species of cacti and spurges (Euphorbia) the leaves 3rc rcpresenred by spines (3.33, 6.9). Starch is commonly stored in the parenchymatous ground tissue of the stem (2.31) and is particularly abundant in the swollen stems of succulents and the underground stems of corms, tubers and rhizomes (6.3). On the condensed shoots of rosette species (4.13) the lea\'es are crowded and the internodes short, bur at flowering the internodes commonly become much more widely spaced as is dramatically shown in Agave (6.2). Anatomy of the mature pnmary stem The vascular system in the young internode usually consists of separate vascular bundles (6.4, 6.5, 6.10, 6.11) that typically form a peripheral cylinder in dicotyledons (1.28) but are scattered in monocotyledons (1.27). The cortex lies external to rhe vascular tissue and is bounded by an epidermis which often bears stomata and trichomes (5.25, 6.5, 6.8). The ground tissue in which the vascular tissue is embedded is basically parenchymatous and the cortex is often photosynthetic (6.6, 6.8, 6.11). in dicotyledons a parenchymatous pith is usually presenr, but vascular bundles occasionally may be present centrally (6.10). In the majority of monocotyledons the bundles occur throughout the ground tissue (1.27), but sometimes a pith is present (6.4). Sclerenchyma fibres are often present in the ground tissue (6.4, 6.8, 6.10) and the parenchyma may become lignified. Collen· chyma frequently occurs JUSt beneath the epider· mis, especially at the angles of the stem (6.5). In some stems a prominent starch sheath occurs in the innermOSt cortical layer and in underground stems this may develop thickening to form an endodermis (6.12). Vascular bundles in the stem are commonly collateral, with the phloem lying nearest to the epidermis and the xylem situated internally and on the same axis (1.11, 6.6, 6.10). Bicollateral bundles may also occur in which the phloem lies both external and internal to the xylem (6.11). in many monocotyledons the bundles are amphivasal with a cenrral strand of phloem surrounded by xylem (6.12). Amphicribral bundles, in which the xylem is surrounded by phloem (6. t3), occur in ferns and a few angiosperms, while in others the bundles may lack xylem. In the great majority of dicotylcdonous stems, a cambial layer is located betwcen the xylem and phloem (6.6, 6.11) but in monocotyledons this is absent (1.11, 6.12). The vascular anatomy at the node is more complex than in the internode due to the branches that pass outwatds from the axial vascular bundles to the leaves and axillary branches (4.17, 4.18,4.23, 6.14). Apart from branching at the nodes, the axial bundles normally interconnect with adjacent vascular bundles at various levels along the internodes. In monocotyledons, axial bundles often run obliquely for some distance in the internode and have frequent interconnections (6.15) with numerous veins (leaf traces) passing outwards to each leaf. In dicotyledons there are usually fewer leaf traces. In species with few interconnections between axial bundles, damage to one part of the axial system may severely disrupt the supply of water and nutrients to parts of the plant lying above or below the injury site. In most stems the protoxylem and protophloem elementS (2.3) 3re damaged during elongation and expansion growth (1.11), so that in the oldet primary stem (3.5, 6.10, 6.11) only the metaxylem and mctaphloem are normally functional. Pericylic 117
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A Colour Atlas of PLA T STRUCTURE B
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5 The green leaf 97 Introduction 97
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• CHAPTER 1 Introduction The asso
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1.6 1.6 L}'copusicon e$culentum (to
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1.17 1.19 ,--------------::c-=-----
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1.22 1.22 Group of rail Cordy/hIe a
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1.32 B 24 1 6 \ -H-r 14 13 c 11 """
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times becomes highly lobed (2.15, 2
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stack (2.14, 2.52) of smooth cister
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2.14 2.14 Diagram of the fine-struc
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2.39 Longitudinally-sl:crionl:d l:h
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CHAPTER 3 Plant histology Disttibut
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3.1 3.2 3.1 TS of the: petrified st
- Page 66: 3.21 ,-------------, 3.23 3.2J Non-
- Page 69: 3.31 TS of n cortienl mucil:lge duc
- Page 72: 3.41 -+-2 3.39 L$ of the phloem of
- Page 78: 3.58 80 3.56 3.56 TS of tbe seconda
- Page 83 and 84: absent or may develop some distance
- Page 85: 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 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 142 and 143: 7.26 7.26 Fine rOOfS from a large t
- 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
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8.64 hnmarure fruir of rhe dleot)·
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a tetraploid h3.S a double: set. Po
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Vacuole An organelle bounded by rhe
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Cell (continued) meiosis 158, 161,
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Sanicula europea (sanicle) 68 Sanse
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