Zea mays

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a tetraploid h3.S a double: set. Polysaccharide A carbohydrate composed of many monosaccharides linked together in a chain, as cenulose and srarch. Polysome A complex of ribosomes concerned with protein synthesis. Primary cell llIall The wall formed by the protoplast up to the end of expansion growth; the cellulose microfibrils are often randomly orientated and nre less abundnnt [han in the secondary wall. Primary thickening meristem This occurs in the subapical region of pbnts WiTh greatly thickened primary stems; divisions throughout the incipient cortex, procambium and piTh lead to rapid radial growth of the a.'
fully expanded leaves. Also a group of ccllulosesynthesising enzymes located ar the plasmalemma. Scale leaf A non-foliage leaf often investing dormant buds or found in underground stems. Schizogeny The separarion of cells along their middle lamellae to form an intercellular sp:lce. Sclereid A type of sclerenchyma cell characterised by its very thick lignified walls and numerous pits; the shape is variable but it is generally mueh shaner than a fibre. Scferenchyma A supporting tissue whose cells arc commonly dead at maturity and possess thick, lignified secondary walls, as in fibres and sclereids. Scutellum The highly modified cotyledon present in grasses which supplies nutrienrs from the endosperm to the germinating embryo. SecondiJry cell wall The wall formed by the protoplast at the end of expansion growth; the cellulose microfibrils are closely crowded and, in anyone layer, lie pacallel to each other (d., primary wall). Secondary walls often become lignified, as in sderenchyma and tracheary elements. Secorulary thickemng This occurs in gymnosperms and moSt dicotyledons and some anomalous monocotyledons. The stem and root increase in diameter due to the formation of sccond:lry vascular tissues by the vascular cambium (or by the secondary thickening meristem), whilst the epidermis is normally replaced by cork formed from the cork cambium. Secondary rhickening meristem In some arborescent monocotyledons (e.g. Dracoeno, Cordyfine) an anomalous form of secondary thickening occurs from a meristem which arises in the outer cortex and Cuts off discrete vascular bundles, plus parenchyma, centripeta11y. Seed The structure which develops from the fertilised ovule; it contains the embryo and a food supply to support early seedling growth. Sepal An outer perianth member which is distinct in form from a petal. Septate (ibre A fihre with thin cross walls which develop after the longitudinal walls have become thickened. Sexine The outermost region of the pollen grains eetine (d., nexine). Shoot The non-rOOt region of the plant; it is usually aerial and composed of the stem bearing numerous photosynthetic foliage leaves (d., root). Sielle area Modified pit fields in the side and oblique end walls of sieve cells or rubes; the plasmodesmata have been transformed into narrow sieve pores and lateral translocation probably occurs via them. Sieve cell The enucleate translocating element in gymnosperms and lower vascular plants, possessing sieve areas on all walls. Sielle plates The transverse or somewhat oblique walls occurring in sieve tubes; it conrains either a single series of large pores or is compound with several series of pores (ct., sieve area). Sil've pore The hole in a sieve are;! or plate through which cytoplasmic continuity occurs from one sieve clement to another; the wall surrounding the pore is commonly impregnated with callose. Sieve tube An elongate clement comprising several to many enucleate cdls interconnected via the sieve plates (former cross walls). Sieve tubes are confined to angiospenns (cL sieve cell). Simple (ruit Formed from the single ovary of an individual flower. Softwood The wood of a conifer which generally lacks thick-walled, lignified fibres; it is therefore easier to saw than most hardwoods. SpoJigy mesophyfl Very Irregular green parenchyma cells with large intercellular spaces bC'twttn them; in bilacial lea\'es this tissue occurs abaxiaUy (d., palisade mesophyll). Sporangium A .structure in which spores are produced; in most fems the spores are uniform in size but in seed plantS different sized spores are produced in mega- and . . mlerosporangl3. Sporl's Haploid cells formed as derivatives of lhe meiotic division of a diploid spore mother cell within a sporangium. Each spore germinates to fOlm the gametophyte. Sporophyte The diploid phase of the life cycle; in vascular plants the sporophpe is dominant (d., gametophyte). Sporopo/lenin The substance composing the exine of pollen grains; it is formed from cyclic alcohols and is highly resistant to microbial decay. Starch The chief food storage polysaccharide of plants composed of several hundred hexose sugars; it is insoluble and accuillulates within rhe stroma of various plastids. Starch sheath In many primary dicotyledonous stems the inner layer of the conical parenchyma forms a sheath with rich deposits of Starch in itS cells. Stamelf The male organ of the flower composed of the terminal amher bearing pollen and the basal sterile filamenr. Stigma The receptive zone of a carpel at the tip of the style, upon which po11en is deposited and germinates. Stipllfes Projections of tissue on either side of the base of the leaf, which in dicotyledons :lre sometimes large and vasculated. Stoma (pI. stomata) A complex consisting of a pore in the shOal epidermis which is surrounded by two specialised guard cells; their turgidity causes the opening 183
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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$culentum (to
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1.17 1.19 ,--------------::c-=-----
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1.22 1.22 Group of rail Cordy/hIe a
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1.32 B 24 1 6 \ -H-r 14 13 c 11 """
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times becomes highly lobed (2.15, 2
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stack (2.14, 2.52) of smooth cister
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2.14 2.14 Diagram of the fine-struc
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2.39 Longitudinally-sl:crionl:d l:h
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CHAPTER 3 Plant histology Disttibut
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3.1 3.2 3.1 TS of the: petrified st
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3.21 ,-------------, 3.23 3.2J Non-
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3.31 TS of n cortienl mucil:lge duc
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3.41 -+-2 3.39 L$ 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
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4.24 4.24 TS of a vascular bundle f
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secretion may temporarily accumulat
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5.3 ,--------------, 5.3 Large fan-
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5.45 5.44 IS of the petiole of the
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5.50 116 5.50 Base of the mature tr
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fibres often develop in the outer p
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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
Page 169: 8.64 hnmarure fruir of rhe dleot)·
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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