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2.6.1.1 Soil texture Literature review Soil is generally comprised of soil particles of various sizes (DONAHUE et al., 1983). Soil texture can be described by granulometry, which is the quantification of the distribution of these soil particles in the different size classes (LECLERC, 2003). These size classes are called the soil separates and they can be placed in three general classes: Sands, silts and clays (Table 2.1) (DONAHUE et al., 1983). Table 2.1: Names of the soil separates and the particle diameters which define them (Modified from DONAHUE et al. (1983)). Soil separate name Diameter range (mm) Stones > 254 Cobbles 75 to 254 Gravels 2 to 75 Very coarse sand 1.0 to 2.0 Coarse sand 0.5 to 1.0 Medium sand 0.25 to 0.5 Fine sand 0.10 to 0.25 Very fine sand 0.5 to 0.15 Silt 0.002 to 0.5 Clay < 0.002 The texture of a soil can be determined after the percentage of each separate within a sample is known and these are then grouped into percentage sand, silt and clay (DONAHUE et al., 1983). These percentages can then be plotted on a triangular graph (See Figure 2.30). The description of the soil is determined by drawing three lines each perpendicular to a side of the triangle and arranged on the axes according to the relative percentages. The description at the point where these lines meet can then be read off. This method can also be used to determine the percentage content of a third separate group if the percentage content of 2 is known. Soil texture has a large influence on plant growth due to its effect on soil water retention capacity, oxygen capacity and thermal conductivity (LECLERC, 2003). Particles larger than 2 mm but less than 250 mm also play a large role in soil texture (DONAHUE et al., 1983). When classifying a soil, the names of these separates precede the rest of the name (e.g. ‘Stony’, ‘silty’ and ‘clay’). 37
Literature review Figure 2.30: A textural triangle showing the range of variation in sand, silt, and clay for each soil textural class (Modified from DONAHUE et al. (1983) and LOVELAND & WHALLEY (1991)). 2.6.1.2 Soil water content Water is a solvent for the soil solution and is essential for plant growth. This depends on the available surface area within the soil, which is determined by soil texture (LECLERC, 2003). In general, soil water content refers to the water that is evaporated by heating soil at 100 to 110 C until no further weight loss is observed (GARDNER et al., 1991). This measurement does however not include structural water, which usually requires heating between 400 and 800 C to evaporate. An example of such structural water is the water molecules which are incorporated with hydroxyl groups in clay lattice structures (GARDNER et al., 1991). In soil water 38
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Propagation of Romulea species Pier
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Contents 2.7 GERMINATION PHYSIOLOGY
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Contents 5.3.1 Explants from seedli
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Abstract The suitability of various
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Declarations I Pierre André Swart,
Page 11 and 12: Declarations DETAILS OF CONTRIBUTIO
Page 13 and 14: Publications from this thesis ASCOU
Page 15 and 16: List of Figures Figure 2.13: Suther
Page 17 and 18: was significantly different from th
Page 19 and 20: List of Tables Table 2.1: Names of
Page 21 and 22: List of Abbreviations 2,4-D 2,4-Dic
Page 23 and 24: Die vlakhaas spits sy oor hy het di
Page 25 and 26: As die mens dan ook so sy dankbaarh
Page 27 and 28: Introduction where a great number o
Page 29 and 30: Introduction The subgenera Romulea
Page 31 and 32: 2 Literature review Leef van daad e
Page 33 and 34: Literature review Figure 2.2: Life
Page 35 and 36: Literature review Figure 2.4: Life
Page 37 and 38: Literature review The plants are sh
Page 39 and 40: Literature review flowers (DE VOS,
Page 41 and 42: Literature review often found on cl
Page 43 and 44: Literature review flowers of R. lei
Page 45 and 46: Literature review flattened upper s
Page 47 and 48: 2.2.16 Romulea tabularis Literature
Page 49 and 50: Literature review extinct, R. papyr
Page 51 and 52: Literature review R. leipoldtii occ
Page 53 and 54: Literature review Figure 2.8: Calvi
Page 55 and 56: Literature review Figure 2.14: Fras
Page 57 and 58: Figure 2.20: Nieuwoudtville weather
Page 59 and 60: Literature review Figure 2.26: Grah
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Page 65 and 66: Literature review Macronutrients ca
Page 67 and 68: Literature review The soils of the
Page 69 and 70: Literature review The embryo is the
Page 71 and 72: Literature review Phase 2 is seen a
Page 73 and 74: Literature review endogenous gibber
Page 75 and 76: Literature review tolerable level (
Page 77 and 78: Literature review these channels pe
Page 79 and 80: Literature review 2.8.7 Seed dorman
Page 81 and 82: Literature review the embryo (COPEL
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Page 85 and 86: Literature review (COPELAND, 1976).
Page 87 and 88: 2.9 BRIEF REVIEW OF IN VITRO CULTUR
Page 89 and 90: Literature review (DEBERGH, 1994).
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Page 95 and 96: Literature review The essential fun
Page 97 and 98: 2.9.3.4 Abscisic acid Literature re
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Page 103 and 104: Literature review and the addition
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Page 107 and 108: Literature review environmental str
Page 109 and 110: 2.11 IN VITRO FLOWERING Literature
Page 111 and 112: Literature review higher regenerati
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Subfamily Ixioideae (continued) Tri
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Literature review Table 2.8: Corm i
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3 Investigation into the habitat of
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Soil sampling and analysis The firs
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Soil sampling and analysis Table 3.
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4 Germination physiology 4.1 INTROD
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4.2.2 Water content and imbibition
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Germination physiology (-N), phosph
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Germination physiology rosea seeds
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Germination physiology Figure 4.4:
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Germination (%) 50 40 30 20 10 0 77
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Germination (%) 100 80 60 40 20 0 c
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Germination physiology The relative
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Germination physiology seeds of R.
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5.2 MATERIALS AND METHODS In vitro
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In vitro culture initiation and mul
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5.2.3 Explant comparison In vitro c
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5.4 DISCUSSION In vitro culture ini
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6 In vitro corm formation and flowe
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In vitro corm formation and floweri
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6.3 RESULTS 6.3.1 Corm formation In
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Commercialization potential of Romu
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Commercialization potential of Romu
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BASKIN, C. C., and BASKIN, J. M. (1
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Literature cited DOWLING, P. M., CL
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Literature cited HILTON-TAYLOR, C.
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Literature cited KUMAR, A., SOOD, A
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Literature cited PIERIK, R. L. M. (
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Literature cited STEINITZ, B., COHE
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