Smaller Inflorescences Research Articles

The pattern of genetic diversity in the Andean grain crop quinoa (Chenopodium quinoa Willd). II. Multivariate methods

Discrete and continuous characteristics related to plant morphology and pigmentation and to the duration of developmental phases were measured or noted in a diverse collection of quinoa germplasm. In a principal component analysis of the continuous characteristics, the first principal component was found to distinguish those accessions which germinate rapidly to produce small plants with small inflorescences, and the second component those which produced a large inflorescence relatively quickly, but there was no clear cut-off between important and unimportant variables or components. A canonical variate analysis of the continuous characteristics provided criteria for distinguishing ecotypes of quinoa, but suggested that these were artificial with the exception of a subtropical type from the Yungas region of Bolivia. A hierarchical cluster analysis of all the characteristics confirmed that the variety Amarilla de Marangani was unusual, but otherwise did not produce clear clusters. Accessions from near sea level in Chile formed a particularly homogeneous group. The impossibility of describing the variation in terms of a few axes or clusters means that a vast range of combinations of characteristics is available to breeders.

Caste‐specific patterns of flower visitation in bumble bees (Bombus kirbyellus) collecting nectar from Polemonium viscosum

ABSTRACT. Foraging routes of worker and queen bumble bees (Bombus kirbyellus Curtis) collecting nectar from flowers of the alpine sky pilot, Polemonium viscosum Nutt., were followed and the corolla tube length, corolla diameter, floral scent, and number of flowers on plants visited or bypassed by bees were monitored. Additionally, the number and proportion of flowers visited per inflorescence and distance flown from each to the next were recorded. Queens and workers differed significantly in choice of flowers. However, intra‐inflorescence visitation rates and departure distances were similar between castes. Castes differed in the extent to which visitation reflected patch quality versus individual floral traits. Both queens and workers failed to visit skunky‐flowered plants more often than they failed to visit sweet‐flowered ones, and preferred large over small inflorescences. However, queens visited large‐flowered plants more often than small‐flowered ones, while workers preferred flowers with shorter corolla tubes, regardless of their diameter. Although a number of studies have documented caste specialization on alternate species of host plants, ours is one of the first to show that morphological preferences promote comparable foraging differences between castes on monospecific plant resources. Queens, once on a plant, responded to floral traits by probing more flowers on large inflorescences, as well as on those with broader floral form. Workers did not alter intra‐inflorescence visitation rate in response to floral traits. For workers, no significant relationship was demonstrated between the likelihood of passing by a plant and the number of flowers probed on the previous inflorescence visited. Thus, workers appeared to accept or reject each plant of P. viscosum independently. However, queens passed by fewer plants when leaving rich inflorescences than poor ones. These results suggest that workers use only individual plant acceptability in choosing which plants to visit, whereas queens base plant choice on patch and individual attributes. Such differences between castes in foraging rules when exploiting the same floral resource have received little attention, and provide insights into the heterogeneity of harvestable reward distributions from the perspective of the forager population.

Pollen flow, self-pollination and gender specialization: Factors affecting seed-set in the tristylous speciesLythrum salicaria (Lythraceae)

Some of the factors governing seed-set in three populations ofLythrum salicaria are examined during two seasons. Plants spatially segregated from legitimate neighbours by distances exceeding 1m set few seeds. Plants with small inflorescences set fewer seeds than those with medium or large inflorescences. Flowers having self pollen applied to the stigma before legitimate pollination set fewer seed per flower than those pollinated with legitimate pollen only. Seeds of the mid-style morph germinated more effectively than those of the long style morph and seeds of the short-style morph showed very low levels of germination.

Two new aroids from Borneo

Bucephalandra giganteaBogner, spec nova, is characterized by its large habit, the relatively small inflorescences and the very slender thecae.Hottarum kinabaluenseBogner, spec nova, is differentiated by its ellipsoid ovaries, the smooth petioles and the absence of staminodes.

Inflorescence Architecture and Flower Sex Ratios in Sagittaria brevirostra (Alismataceae)

Two populations of Sagittaria brevirostra from the same lake were sampled 10 years apart and yielded similar data on inflorescence structure and on numbers and ratios of male and female flowers. Larger inflorescences have relatively more male than female flowers than do smaller inflorescences. Pollination success is unrelated to inflorescence size or sex ratio within an inflorescence.

INFLORESCENCE ARCHITECTURE AND FLOWER SEX RATIOS IN SAGITTARIA BREVIROSTRA (ALISMATACEAE)

Two populations of Sagittaria brevirostra from the same lake were sampled 10 years apart and yielded similar data on inflorescence structure and on numbers and ratios of male and female flowers. Larger inflorescences have relatively more male than female flowers than do smaller inflorescences. Pollination success is unrelated to inflorescence size or sex ratio within an inflorescence.

The occurrence of polysety in relation to the number of archegonia in the female inflorescences ofPhascum cuspidatumHedw.

AbstractIn Phascum cuspidatum the number of sporophytes per inflorescence was found to increase, up to a certain limit, with increase in the number of archegonia present. The number of archegonia present varies with the age of the inflorescence, and fertilization terminates the production of archegonia. The common occurrence of solitary sporophytes is due to fertilization at a time when only a small number of archegonia is present in most inflorescences. Delayed fertilization, leading to an increase in the average number of archegonia per inflorescence, is a necessary precondition for increased occurrence of polysety. As many as five sporophytes in a single inflorescence formed capsules with spores without significant reduction in the size of capsules. Variation in the frequency of abortive embryos gave evidence of competition amongst sporophytes and this was most severe in the smaller inflorescences. The occurrence of polysety in Tortula muralis appears to be governed by the same rules.

Origin, Cytology, and Reproductive Characteristics of Haploids in Pearl Millet1

AbstractPearl millet [Pennisetum americanum (L.) K. Schum.] is an important introduced forage species in the U.S. Thirteen haploid plants with seven chromosomes in somatic cells were studied. Two plants resulted from a twinembryo caryopsis, whereas the others were discovered in field plantings. The rate of spontaneous haploid occurrence was 1 per 10,000 plants in the inbred ‘Tift 23A.’ Seed set on individual haploid plants ranged from 502 to none. No haploids were recovered from progeny of seeds harvested from haploid plants. Spontaneous chromosome doubling occurred in several plants. The doubled sectors in the inflorescences were characterized by good exsertion and good dehiscence of anthers. Haploids were conspicuous because of their small inflorescence diameters, narrow leaves, and poor exsertion and dehiscence of anthers. Meiotic chromosomes of haploids were mostly univalents, but occasional pairing of two or more chromosomes was observed at metaphase I.

Adaptive Design of the Floral Display in Asclepias syriaca L.

In the common milkweed, inflorescence size above a certain size is not correlated with seed set or pollination rates. The number of pods matured by each inflorescence is limited, and a minimum number of flowers appear to be necessary to ensure that pod production, within this limit, is maximized. Inflorescences larger than this optimum size for pod production may have particular selective value in contributing pollinia to other plants. The balance between the high-cost (per fruit), low-risk strategy of producing small inflorescences for pod production and the low-cost (per set of pollinia), high-risk strategy of large inflorescences for increasing pollinia production is probably adaptive. The partitioning of flowers among separate inflorescences permits an increase of pod production and may provide advantages from the temporal dispersion of blooming. INTRODUCTION Insect-pollinated plants have a great variety of evolutionary choices in the design of their floral displays. The flowers on a stem may be clustered in space and/or time, and flowering stalks may themselves be clumped in various ways and densities. The success of any floral display must be measured in terms of the number of viable offspring produced, which is likely to be a function of success in attracting effective pollinators and, perhaps, dispersers, and the avoidance of predators (Yeo, 1972). Burtt (1961) began to explore some of these relationships for Compositae, but little other work has been published on the evolution of floral arrangements. However, the general problem of the evolution of flowering strategies is attracting growing attention (e.g., Beattie et at., 1973; Heinrich and Raven, 1972; Janzen, 1971; Stebbins, 1970, 1971; Willson, 1972, 1973). The success of various flower arrangements, measured in terms of pollination and seed set, was examined as a function of clustering of flowers, pollination rates and predation. METHODS A. syriaca has small pinkish flowers displayed in simple, compact, many-lowered umbels, often several on each flowering stalk, and the fruit pods may-contains hundreds of seeds. Over 60 milkweed plants were sampled beginning in late June at the commencement of blooming.

INVESTIGATIONS ON THE SPORTING PROCESS IN GREENHOUSE CHRYSANTHEMUMS

The chromosome numbers of 56 varieties of greenhouse chrysanthemums were determined. Fifty-one varieties belonged to 10 'families' of sports and the chromosome numbers of the sports were compared with those of their vegetative parents. Sporting, mostly flower colour mutation, was accompanied by the gain or loss of a few chromosomes in about 30 per cent of the cases. Two plants with different chromosome numbers but with the true varietal flower colour were found.The most frequent chromosome number in the authors' material was 2n = 57. The range was 2n = 45–64. Mitotic irregularities and chromosome number variation within individuals were observed. Attempts to induce sporting by hot water treatment failed.Varieties with large inflorescences had higher chromosome numbers (2n = 58–64) than varieties with medium or small inflorescences (2n = 54–58), but in most of the material varieties with small inflorescences differed little in chromosome number from those with medium-sized inflorescences. Five additional varieties with very small inflorescences had lower chromosome numbers (2n = 45–55).