Indeterminate Inflorescences Research Articles

Floral Biology of Myristica fragrans Houtt. (Myristicaceae), the Nutmeg of Commerce

The flowering and pollination of Myristica fragrans were studied on plants cultivated in southern India. The staminate flowers are borne in indeterminate inflorescences and function only for a single night. Pistillate flowers are borne solitarily and appear receptive for 2-3 days. Staminate plants may produce over 50 times as many flowers as pistillate plants. Both types of flowers are strongly fragrant. A single species of beetle, Formicomus braminus (Anthicidae, ant-mimicking flower beetles), appears to be the best candidate for an effective pollinator of nutmeg in the area of the study, although other species of small beetles may be involved. The beetles are strong fliers, are active nocturnally around staminate flowers, and carry significant pollen loads. Pollen is the only evident pollinator reward. Pistillate flowers produce no reward, and spatial constraints of the perianth and stigma appear to prevent beetles from entering the flowers. Pollen carried on the beetle's head or body would be deposited on the stigma when the insect attempts to enter the flower. This is the first report of a food-deception automimicry in a cantharophilous pollination system. The pollen/ ovule ratio for M. fragrans is estimated to be 801,000/1, a very high P/0 ratio for an insect-pollinated plant. THERE ARE SEVERAL REASONS TO SUSPECT that the four Southeastern Asian genera of Myristicaceae may be beetle pollinated. These include (1) the predominance of white or cream to light-yellow flowers, (2) strong nocturnal fragrance, (3) lack of well-defined nectaries or other secretory structures (Wilson & Maculans 1967, Armstrong & Wilson 1978) (although reports of nectaries persist, e.g., Cobley 1976), and (4) the prevalence of beetle pollination among other members of the Annonales (Thien 1974, 1980; Faegri & van der Pijl 1979). However, flowers of Myristica, Horsfieldia, Knema, and Gymnacranthera differ morphologically from typical beetle-pollinated, annonalean flowers in several important respects. These genera are dioecious, as are all Myristicaceae, although there are reports of monoecious species in Iryanthera (Smith 1937). The flowers are small and do not form a broad cup or saucer. Pistillate flowers have one simple pistil containing a single ovule. Androecia consist of few to many, variously fused stamens rather than numerous, free, leaf-like stamens. In several genera, including Myristica, the perianth is fused into an urn-shaped enclosure. These differences suggest that Myristicaceae have either a nonbeetle pollinator or a different type of cantharophilous syndrome. Most accounts of nutmeg biology (e.g., Mcllroy 1967, Purseglove 1968, Cobley 1976) assume that pollination is effected by small insects, although wind pollination also is considered possible (Mcllroy 1967), and one researcher suggested that moths (Lepidoptera) are pollen vectors of M. fragrans (Deinum 1949). Pollen vectors of other annonalean families (Winteraceae, Degeneriaceae) include Diptera, Thysanoptera, primitive Lepidoptera, and Coleoptera (Thien 1980). In this study of M. fragrans we present preliminary information about the floral biology and pollination ecology of Myristicaceae. Specifically we made field observations and manipulated plants to determine (1) the phenology of staminate and pistillate flowers, (2) the relative abundance of staminate and pistillate flowers, (3) the nature of floral attractants and pollinator rewards, and (4) the identity and behavior of the effective pollinator.

Zonation in the shoot apex ofMatthiola incana R. Br.

Zonation in the shoot apex ofMatthiola incana was studied histochemically from the mature embryo to flowering. The plumular apex of the mature embryo shows a single-layered tunica covering a homogeneous mass of cells. The first evidence of zonation is seen in the shoot apex of the 2-day old seedling. Zonation is well established on the fourth day after seed wetting with a single-layered tunica covering a lightly stained central mother cell zone, a subjacent pith meristem and a densely stained peripheral zone. In the transitional apex zonation is less marked and there is increased stratification. At 6-weeks, the apex changes into the indeterminate inflorescence apex showing acropetally developing floral primordia. The axially located cells of the inflorescence apex are lightly stained. The histological and histochemical data indicate that zonation resembling that in the vegetative apex is retained to a lesser degree in the inflorescence apex as well.

Origin and Development of Secondary Capitula inCalendula officinalisL. in Response to Gibberellic Acid

Foliar application of gibberellic acid greatly enhanced the formation of secondary capitula. The proportion of primary capitula showing this feature increased from 6% in the controls to 28, 58, and 54% at 100, 250, and 500 parts 106 GA3, respectively. Secondary capitula were initiated either along the periphery or in the centre of the receptacle or from both; their total numbers for 15 plants per treatment were 53, 215, 660, and 404 in response to 0, 100, 250, and 500 parts 10~6 GA3, respectively. Secondary capitula were smaller and had fewer disc florets and fruits, particularly of the 'wingless and small' type. Tertiary capitula, not observed in nature, formed on 2-72 and 3-21% of the secondary capitula on plants sprayed with 250 and 500 parts 10~6 GA3. The formation of a secondary inflorescence meristem in treated plants in place of a floret primordium can be detected histologically early in its development, and its pattern of development resembles that of the primary capitulum. INTRODUCTION Scotch marigold (Calendula officinalis L.) is grown as a winter annual in Delhi. In this plant the shoot apices of the main axis and the axillary branches terminate in heterogamous capitula. The ray florets are unisexual (female) and produce polymorphic fruits of the following types; sickle-shaped spiny; double-winged; single-winged; and wingless and small. The disc florets are bisexual but are functionally male. About 6% of the capitula borne by the 'double yellow' variety have been observed to bear smaller secondary capitula with fewer involucral bracts, florets, and fruits. It was of interest to study possible factors converting a determinate to an indeterminate inflorescence meristem. Bose and Nitsch (1970) reported the formation of secondary capitula in scotch marigold in response to gibberellic acid. The present work was designed to study quantitatively the effect of exogenously applied gibberellic acid on the origin and development of secondary and tertiary capitula. MATERIAL AND METHODS Two to 3-week-old seedlings of Calendula officinalis L. (double yellow) raised in a nursery bed in mid-October were transplanted to soil in 25 cm pots. This content downloaded from 157.55.39.144 on Wed, 07 Sep 2016 06:27:15 UTC All use subject to http://about.jstor.org/terms 654 Mohan Ram andMehta—Secondary Capitula in Calendula Young plants under outdoor conditions having 10-12 leaves (just after floral evocation) were given three foliar sprays of gibberellic acid (100, 250, and 500 parts 10~6) at 10 d intervals. There were 15 replicate plants per treatment. All sprays, including water controls, contained Triton X-l 14 (0-01%) as wetting agent. Inflorescence apices were fixed in 4% (w/v) aqueous formaldehyde at pH 7, dehydrated through ethyl alcohol-xylene, and embedded in a mixture of paraffin wax and Histowax (3:1, by vol.). Serial sections, 10 /xm thick, were stained with haematoxylin and counterstained either with orange G or erythrosin. The pattern of branching of the plant and the location of the capitula are shown in Plate 1. PBCj Tc-m m -