Special Modes of Shoot Organization in Monocotyledons

I'seudostems. It is well-known that in Musaceae «1 nd Veratrum successively embracing sheaths of

Fig. 8A-K. Collar and root formation in monocotyiedonous seedlings. A-C Galtonia candicans. A Seedling with fully developed cotyledon, the furrowed surface of the primary root indicating root contraction. B Cotyledon base, detail of A. C Same at a somewhat later stage, the first shoot born root piercing its coleorhiza. D Allium ascalonicum, the first shoot born root emerging. E Aphyllanthes monspeliensis, emergence of shoot born roots. F Butomus umbellatus, collar densely covered with collar rhizoids. G Anigozanthos manglesii, numerous shoot born roots accompanying the weak primary root H Potamogeton nodosus, the collar (only a few rhizoids indicated) covering lower surface of thick storage hypocotyl, primary root only weakly developed. I Tillandsia butzii, with rudimentary primary root J Maranta sp., collar roots emerging from massive collar, primary root arrested. K Pistia stratiotes, primary root missing, c Collar; co cotyledon; cp coleoptile; cr coleorhiza; k haustorium; hy hypocotyl; p root pole; pi eophyll; pr primary root; sr shoot born root; r rudiment of primary root; rh collar rhizoids; vl median vaginal lobe of the cotyledonary sheath foliage leaves form an upright stemlike shoot -actually a special type of a leaf rosette. In the vegetative phase the axis proper is represented by the sturdy rhizome, and only with the onset of

Veratrum Album Rhizoma
Fig. 9A-C. Pseudostems in monocotyledons. A Musa X sapietitum, habit. B, C Veratrum album. B Habit C Schematic longisection. A', B' Cross-section of the pseudostem. Not to scale. (A, A' Dahlgren et al. 1985; B, B', C Troll 1954)

flowering does the inflorescence axis push its way through the sheath complex to bring the flowers above the leaves (Fig. 9).

Special Modes of Branching. Generally, the monocotyledons bear 1 bud axillary and in a median position with respect to the subtending leaf, but there are exceptions to this rule. An interesting case was reported by Fisher (1978) and Fisher and Dransfield (1979). In Musa and in rattan palms (Daemonorops spp. and Myrialepis scortechinii), they found the lateral buds opposite the leaf axil (Fig. 10B,C). Since in rattans these buds are subtended by the tubular sheath of their subtending leaf, it is difficult to explain this unusual position as being caused by a pronounced concaulescence, i.e., that this bud could belong to the preceding leaf. In Korthalsia rigida the vegetative buds are 130° to the axil, interjnediate between the normal and the leaf-opposed position.

Collateral accessory buds are scattered in monocotyledons. A well-known example is garlic (Fig. 10D,E). Here a whole group of daughter bulbs represents 1 normally positioned median axillary bulb and a number of additional collateral bulbs. Similar arrangements are found in other Allium species (Irmisch 1850, 1876; Fig. 10F). The numerous small corms developed at the base of a Gladiolus corm are also produced from collateral buds. Collateral flowers are produced in the axils of the large bracts of the Musa inflorescence.

Another strange mode of branching is the di-chotomous forking of the apical meristem. This phenomenon was first reported by Schoute (1909) for the palm genus Hyphaene. It has taken more than 60 years for additional examples to be found (see Fig. 10A). Detailed analyses are now available for Flagellaria indica (Tomlinson 1970a, Tomlinson and Posluszny 1977), Nypa fruticans (Tomlinson 1971), Chamaedorea cataractarum (Fisher 1974) and Strelitzia reginae (Fisher 1976). Uhl and Dransfield (1987) listed six palm genera with dichotomizing apices. There is every indication that in all these cases the branching is initiated by a true bifurcation of the apex. This mode of branching is likely to be derived rather than ancestral in monocotyledons.

A further unusual branching pattern is found in many bamboos. The axils of the sheathing scales along the culm bear "branch complements", which often are difficult to interpret morphologically (Fig. 10H). In some cases, they appear to be a telescoped, much branched axillary shoot system which originates from a single axillary bud. In other cases, a series of accessory buds seems to be developed (McClure 1966). To understand these complex systems, detailed developmental analyses are needed.

Phyllocladia. Assimilating, axillary organs in Asparagus (Fig. 40), Ruscus, Semele, and Danae (Fig. 116) have been subject to controversial interpretations. Arber (1924a) gives an extended overview of the older literature. Several authors thought that these organs are pseudoterminal leaves, in some instances fused with inflorescences (see Velenovsky 1903, Arber 1924a, Schlittler 1953,

Nypa Fruticans

I'lg. 10A-H. Special modes of branching in monocotyledons. A Oichotomous branching. A Nypa fruticans. B, B', C Leaf-opposed bud initation in Musa. B Musa coccinea, two views of I ho same plant base, B' Diagram of bud position. C Musa troglodytarunty detail of bud. D-H Collateral accessory buds. I) Allium sativum, bulb from above. E Diagram of D. F Allium vineale, daughter bulb with five accessory bulbs. G Musa chinensis, two series of collateral flowers in the axil of a large bract, adaxial view. H Arthrostylidium harmonicum, basal portion of a fully developed mid-culm branch complement. Some figures modified. Not to scale, b Bud; sh sheath of subtending leaf to leaf-opposed bud; lb leaf-opposed bud. (A Tomlinson 1970; B, B', C Fisher 1978; D, E, G Troll 1948; F Irmisch 1850; H McClure 1966)

Fig. 11A-H. Rhizomes and runners in monocotyledons. A Neoregelia ampullacea, sympodially connected generations of runners. Each sympodial unit consisting of a plagiotropic, scale-leaved runner and a distal orthotropous rosette of foliage leaves. Arrows indicate the change in growth direction for each sympodial unit B Digitaria pertenuis. Runner growing monopodially for a long distance. C, D Two principal forms of rhizomes in bamboos. C Arundinaria amabilis, monopodia], leptocaul rhizome. D Bambusa beecheyana, sympodial, pachycaul rhizome. E Sagittaria lancifolia. Monochasial rhizome, upper view, erect leaves cut off to show scars of previous terminal inflorescences (inf). F, G Polygonatum multiflorum. F Flowering plant. G Rhizome from above. H Rhizome of Iris pseudacorus. Depending on whether the plant comes to flower or not, annual rhizome units are added sympodially after flowering, monopodially without flowering. Some figures modified. Not to scale. (A Rauh 1990; B Gilliland 1971; C, D McClure 1966; E Tomlinson 1982; F, G Troll 1943; H Rodionenko 1961)

Seedling Organization Monocotyledons

I960). In Asparagus subgen. Myrsiphyllum Arber (1924b) interpreted these organs as being prophylls of an axillary shoot the axis of which is completely abortive, while in Asparagus s. str. she (hought that they are axial organs. Most mor-phologists accepted the idea that the organs in question are axial structures, i.e., phyllocladia. This interpretation is strongly supported by developmental studies of Kaussmann (1955), Hirsch ( 1977), and Barykina and Gulenkova (1985).

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  • sinit nasih
    Where are prophylls and rhizoids?
    8 years ago

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