Multiple Inflorescences Research Articles

Floral Ontogeny of Pelargonium × domesticum

Floral ontogeny of Pelargonium xdomesticum was examined for two cultivars grown under identical environmental conditions. Apical meristems of `Duchess' and `Jennifer' were vegetative at the commencement of the experiment. Meristems were examined every five days over an experimental period lasting 85 days. Floral ontogeny was the same for both cultivars, although the timing of floral initiation of the meristem, floral organ initiation, and floral organ development differed. The vegetative meristem was convex with leaf primordia initiated on either side in an alternate pattern. Early floral initiation was characterized by formation of a cleft towards one side of the meristem, followed quickly by a second cleft on the other side. Between the clefts new meristems developed. New meristems lacked leaf primordia. Proliferation of meristems continued until numerous meristems were organized in a cluster arrangement at the apex of the shoot. Proliferation of meristems at the apex continued until multiple inflorescences had developed. Inflorescences were subtended by bracts. Floral organ primordia were initiated in a succession of four whorls: sepals, petals, androecia and gynoecium. Petals and androecia appeared to develop simultaneously soon after sepal primordia were visible. Petal primordia remained small while the androecia continued to grow. The gynoecium first formed a conical shape, with carpels protruding from the base in a bulbous fashion. At the distal end of the gynoecium, divisions appeared which developed into stigmatic lobes. As the gynoecium elongated, stigmatic lobes became more pronounced. Petal elongation concurred in synchrony with elongation of the gynoecium. On one experimental unit of `Duchess' two florets had opened at 750 total cumulative moles. No `Jennifer' florets had opened by termination of the experiment.

Survey of Shoot Organization in the Araceae

Shoot organization is examined in 87 species from 29 genera representing all six subfamilies of the Araceae and of Acorus, which has been placed in a separate family. Within each taxonomic group examined, the details of shoot organization are presented, including the types of segments and articles which make up the shoot, the degree of expansion of leaf blades, and the placement of buds along the shoots. Literature on shoot organization of the 29 genera is reviewed. The degree of correlation between shoot organization characteristics and systematic groupings is examined, and the utility of these characteristics for systematics is evaluated. It is found that within the taxa observed, the pattern of shoot organization provides a distinctive “fingerprint” at the generic or sectional level, sufficient for determination of the group. Some patterns which appear are pointed out: taxa with bisexual flowers usually produce a single inflorescence at the terminus of a vegetative article. A few taxa with bisexual flowers produce pairs of inflorescences at the ends of articles. Multiple inflorescences (more than two) at an article terminus occur only among taxa with unisexual flowers. Multiple inflorescences are associated with anisophyllous or homeophyllous sympodial growth, while single or paired inflorescences are associated with homeophyllous or intermittent homeophyllous sympodial growth. These patterns might be understood as the result of selection for flexibility of reproductive effort and of seasonal reproduction.

SURVEY OF SHOOT ORGANIZATION IN THE ARACEAE

Shoot organization is examined in 87 species from 29 genera representing all six subfamilies of the Araceae and of Acorus, which has been placed in a separate family. Within each taxonomic group examined, the details of shoot organization are presented, including the types of segments and articles which make up the shoot, the degree of expansion of leaf blades, and the placement of buds along the shoots. Literature on shoot organization of the 29 genera is reviewed. The degree of correlation between shoot organization characteristics and systematic groupings is examined, and the utility of these characteristics for systematics is evaluated. It is found that within the taxa observed, the pattern of shoot organization provides a distinctive “fingerprint” at the generic or sectional level, sufficient for determination of the group. Some patterns which appear are pointed out: taxa with bisexual flowers usually produce a single inflorescence at the terminus of a vegetative article. A few taxa with bisexual flowers produce pairs of inflorescences at the ends of articles. Multiple inflorescences (more than two) at an article terminus occur only among taxa with unisexual flowers. Multiple inflorescences are associated with anisophyllous or homeophyllous sympodial growth, while single or paired inflorescences are associated with homeophyllous or intermittent homeophyllous sympodial growth. These patterns might be understood as the result of selection for flexibility of reproductive effort and of seasonal reproduction.

Overcompensation in Response to Mammalian Herbivory: The Advantage of Being Eaten

Plants of scarlet gilia, Ipomopsis aggregata, are exposed to high levels of mammalian herbivory (by mule deer, Odocoileus hemionus, and elk, Cervus elaphus) early in the season, before flowering. During this period of our study, up to 56% of all individuals experienced a 95% reduction in aboveground biomass. Browsed plants rapidly responded by producing new inflorescences and flowering within 3 wk. Unbrowsed plants produced only single inflorescences, whereas browsed plants produced multiple inflorescences. Field observations and experimental manipulations showed that plants with multiple inflorescences produced significantly greater numbers of flowers and fruits than unbrowsed individuals. Because there were no differences between browsed and unbrowsed individuals in the number of seeds produced per fruit, seed weight, subsequent germination success, and survival, browsed plants enjoyed a 2.4-fold increase in relative fitness. Consequently, there is an immediate reproductive advantage to being eaten. Und...

Pollination, Predation and Seed Set in Linaria vulgaris (Scrophulariaceae)

Linaria vulgaris, a self-incompatible perennial herb, has a complex of adaptations related to insect-pollination. These include: (a) the production of conspicuous yellow flowers, each with a bright orange palate, arranged in vertical inflorescences of 15-20 flowers; (b) the production of multiple inflorescences by individuals. These flower in a staggered, but temporally overlapping, sequence suggesting a trade-off between maximum showiness and maximum blooming period; (c) the production of nectar containing 37% sugar, as sucrose equivalents. Despite these adaptations, however, Linaria vulgaris has low seed set when compared to most other self-incompatible perennials that have been studied. The success of ovules declined from ca. 1.6%o in early August (the height of the season for this species) to ca. 0.3% in early September, although individuals continued to produce new flowers until the end of September. The declining seed set occurred at a time when pollinator activity was declining. It is clear that predispersal seed predation by insect larvae was important in limiting seed set. Heavy predation of ovaries, however, made it difficult to assess the relative importance of pollinator availability as an additional limiting factor. INTRODUCTION Recently, there has been considerable interest in the features of flowering plants that make them attractive to pollinators. One of the questions investigated has been the extent to which seed set in self-incompatible plant species is pollinatoror predatorlimited. Schemske et al. (1978) showed that such limitation is a factor in six selfincompatible spring woodland herbs, which set fewer seeds under natural conditions that when hand-pollinated. Barkham (1980) suggested that seed set in Narcissus pseudonarcissus is severely pollinator-limited. Silander and Primack (1978), however, concluded that pollinator service was adequate to achieve complete seed set in Oenothera fruticosa. Zimmerman (1980a) reported that pollinator service was adequate to achieve a high level of seed set in Polemonium foliosissimum in the early part of its flowering season, but that pollinators were a limiting resource later in the season. Zimmerman (1980b) also reported that the seed predator, Hylemya sp., of P. foliosissimum caused high seed mortality in ovaries of flowers that had received a large number of pollinator visits and, as a result, set many seeds. This paper describes the pollination ecology of Linaria vulgaris Mill. (Scrophulariaceae). The research was designed to answer four questions: (1) How attractive are flowers of this species to pollinators; (2) What is the success rate for ovules of this species; (3) How available and effective are the pollinators; and (4) Is predation an important factor in limiting seed set? Linaria vulgaris is a rhizomatous perennial which is widespread along roads, railroad tracks and waste places throughout the United States. It is believed to have been deliberately introduced into eastern North America as an ornamental soon after the arrival of European settlers and has become a serious weed in some places, especially W of the Rocky Mountains. The flowers are strongly zygomorphic, yellow with a bright orange palate, and arranged in racemose inflorescences of 15-20 flowers. Each flower has a spur 15-20 mm long in which nectar collects. MATERIALS AND METHODS