Floral Form Research Articles

POLLEN-PISTIL RELATIONSHIPS IN THE POLEMONIACEAE.

The multitude of floral architectures within angiosperms are complex adaptations (or adaptive strategies) insuring the transfer of pollen from a plant to another of the same species, the subsequent growth of the pollen tube in the style, and the fertilization of the ovule. During the past decade, ecologists and evolutionists have learned much about floral structure in relation to biotic and abiotic dispersal agents of pollen, specifically how the shape and sizes of flower parts optimize pollen transport and deposition by various pollinators (Kugler, 1970; Frankel and Galun, 1977; Faegri and van der Pijl, 1979; Cruden and Miller-Ward, 1981). Much more attention has been given to floral syndromes in relation to pollinators than to the integrated evolution of floral components, even though it is apparent that if the system is to remain functional, most evolutionary alterations in one component must be compensated for by changes elsewhere. Studies on that aspect have been rather few (Galinat, 1961; Pandey, 1971; Lee, 1978; Cruden and Miller-Ward, 1981). Many plant families have undergone extensive radiation in pollination biology, and correspondingly in floral form and size. Some of the changes are in characteristics involved in pollinator attraction; others are in characteristics immediately involved in pollen presentation, transfer and receipt. The position of stigmas is a notable example in the latter category. In species which are bird-pollinated stigmas may be exserted, whereas in butterfly-pollinated relatives the stigmas may be deep within the corolla tube; in bee-pollinated relatives stigmas may be near the orifice of the corolla tube. The position of the stigma is determined by the length of the style. Although this position is pivotal in maximizing pollen receipt, the great diversity in style length (10-fold differences in many genera) receives relatively little attention. Similarly, pollen characteristics and diversity have been described at length with an emphasis either on their taxonomic value (Erdtman, 1969, 1970) or on their biochemistry and physiological function (Barbier, 1970; Heslop-Harrison, 1971, 1979; Stanley and Linskens, 1974; Muller, 1979). Given that pollen grains must send tubes through the style on their way to the ovule, we may ask whether differences in style length are accompanied by differences in some attribute of pollen, and whether changes in style length of necessity are accompanied by changes in pollen. In general, the germination of pollen and growth of the tube are conditioned by the components of the pollen grain, as by physiochemical processes involving stigma and style (Rosen, 1971; Stanley, 1971; de Nettancourt, 1977; Heslop-Harrison, 1978, 1979; Clarke et al., 1979). The pollen may contain carbohydrates and lipids in several forms, enzymes, membranes, and amino acids, all of which are essential for germination and growth; however, many of them are not synthesized during tube growth. Some nutrients, such as polysaccharides and amino acids, can be absorbed from the style, whereas some other materials (especially m-RNA) cannot be obtained this way and thus function as limiting factors (Barbier, 1970; Mascarenhas, 1971, 1975; Stanley, 1971; Vasil, 1974). Since many similar provisions for growth must be present in the pollen grain

Observations on anthocyanin pigmentation in seedlings and mature plants of Impatiens capensis and its possible role as a determinant of floral form

Plants of Impatiens capensis Meerb. were observed in the field for the presence or absence of anthocyanin pigmentation. Seeds were collected at a site where cross-pollination between plants with orange spotted flowers (forma capensis) and plants with orange unspotted flowers (forma immaculata) was highly likely to have occurred. Spotted and unspotted flowers were found to possess a similar array of carotenoids in similar concentrations, but cyanidin glycosides were found only in extracts of spotted flowers. Progeny of spotted flowers were 98% anthocyanin-producing in root tips, roots, hypocotyl, and cotyledons of seedlings (photographs of the unusual development of seedlings are presented). Only a minority of progeny of unspotted flowers were cyanic. One of these cyanic offspring of unspotted flowers was grown to maturity and produced 75% cyanic seedlings when selfed. Under cultural conditions where crossing had been prevented, spotted-flowered plants produced only cyanic seedlings and unspotted-flowered plants produced only acyanic seedlings. All these observations suggest that the presence of anthocyanin pigmentation is a dominant, heritable characteristic of I. capensis forma capensis and its absence a recessive, heritable characteristic of I. capensis forma immaculata and that it is this feature only that distinguishes these two formae.

Chromosome studies in species and hybrids ofPetrorhagia sect.Kohlrauschia (Caryophyllaceae)

Cytogenetic investigations have been made in the fourPetrorhagia species and hybrids of the sectionKohlrauschia. The three diploid species show close similarities in chromosome number, size and morphology, with the exception ofP. velutina, where one pair of metacentric chromosomes is represented by a pair of telocentrics. Meiotic studies in hybrids indicate close genomic homology between the diploid species and also between the two floral forms ofP. prolifera. The tetraploidP. nanteuilii behaves as an allotetraploid forming only bivalents at meiosis and results suggest thatP. velutina andP. prolifera are the diploid progenitors of this species. Since meiosis in diploid and triploid hybrids results in extensive intergenomic pairing it is concluded that the natural tetraploid has a bivalent promoting mechanism that prevents pairing between the genomes of its diploid progenitors.

Cleistogamy: A tool for the study of floral morphogenesis, function and evolution

Cleistogamy—the production of open (chasmogamous—CH) and closed (cleistogamous—CL) floral forms by a species—is widespread among the angiosperms. While the CL flower is autogamous, the CH flower may provide a means for outcrossing. The term “cleistogamy” has also been used to describe other phenomena. A classification of types of cleistogamy is proposed. In this review, a restricted definition of cleistogamy is used to refer to species which show real floral dimorphisms, with divergent developmental pathways leading to CL and CH as well as intermediate floral forms. Reductions in the androecium and corolla are the most common feature of the CL flowers. The structural, developmental, and functional aspects of cleistogamy are reviewed. Evidence is presented to show that the CL flowers have modifications in their development which ensure self pollination. A proposal is made for using this phenomenon of dimorphic flower production as a system for the study of floral morphogenesis, function and evolution.

Pollination biology of heteromorphic populations of Oxalis alpina (Rose) (Oxalidaceae) in south-eastern Arizona

In south-eastern Arizona, heterostylous (often trimorphic) populations of Oxalis alpina (Rose) Knuth are visited most commonly by females of the solitary bee Heterosarus bakeri Cockerell. Bees collect pollen from flowers and are presumed to be the major pollinators of O. alpina in this region. Analysis of pollen loads from the corbiculae of H. bakeri suggests that individual bees may specialize temporally on different floral forms. However, the apparent preferential collection of pollen probably results from spatial segregation of morphs and the localized foraging behaviour of bees rather than preference on the part of individual bees for particular stylar forms. As a group, bees appear to visit floral morphs of O. alpina indiscriminately, even though individual bees may have a preponderance of pollen from one morph type. Despite spatial segregation leading to pollinator flights between members of the same incompatibility group, capsule and seed production in populations of O. alpina is high for all forms. Loss of the mid form in some populations cannot be attributed to pollinator preferences for individual style morphs.

Pollination biology of heteromorphic populations of Oxalis alpina (Rose) (Oxalidaceae) in south-eastern Arizona

In south-eastern Arizona, heterostylous (often trimorphic) populations of Oxalis alpina (Rose) Knuth are visited most commonly by females of the solitary bee Heterosarus bakeri Cockerell. Bees collect pollen from flowers and are presumed to be the major pollinators of O. alpina in this region. Analysis of pollen loads from the corbiculae of H. bakeri suggests that individual bees may specialize temporally on different floral forms. However, the apparent preferential collection of pollen probably results from spatial segregation of morphs and the localized foraging behaviour of bees rather than preference on the part of individual bees for particular stylar forms. As a group, bees appear to visit floral morphs of O. alpina indiscriminately, even though individual bees may have a preponderance of pollen from one morph type. Despite spatial segregation leading to pollinator flights between members of the same incompatibility group, capsule and seed production in populations of O. alpina is high for all forms. Loss of the mid form in some populations cannot be attributed to pollinator preferences for individual style morphs.

HAWKMOTHS AND THE GEOGRAPHIC PATTERNS OF FLORAL VARIATION IN AQUILEGIA CAERULEA.

The correlations between certain floral characteristics of plant species and the kinds of animal pollen vectors that visit their flowers are well known. The functional basis for the convergence of floral forms and colors has long been recognized, and terms such as bumblebee and hummingbird are commonly used (Macior, 1971; Proctor and Yeo, 1972; Faegri and van der Pijl, 1979). On the other hand, relatively few plant species are visited by only one kind of potential pollinator, exhibiting instead what Macior (1971) referred to as an of pollinators. Although the flowers of a particular plant population are visited by a characteristic array of potential pollen vectors, the spectrum of effective pollinators may be different for populations in other habitats, at different elevations, or elsewhere in the species' geographic range. If the selective pressures exerted by floral visitors on different populations of a species are consistently dissimilar, distinct races may develop. Grant and Grant (1965) reported this pattern of differentiation to be common in North American members of the Polemoniaceae. Variation in flower color often occurs both within and between populations of a plant species, and in some cases there is evidence that color morphs differ in their relative attractiveness to potential pollinators as in Lantana (Dronamraju, 1960), in Leavenworthia (Lloyd, 1969), in Phlox (Levin, 1972), in Cirsium (Mogford, 1974), and in Raphanus (Kay, 1976). Thus flower color polymorphisms within a plant species may reflect adaptation by different populations to different pollination conditions. Kay (1978) and Mogford (1978) have reviewed the literature on flower color polymorphisms and pollinator behavior. This paper examines the geographic distribution of flower color and spur length in populations of Aquilegia caerulea, the Colorado Columbine, in western North America and considers these patterns of floral variation in relation to the composition of the pollinator fauna in different portions of the range of the species.

The floral biology and seed production of Nymphoides peltata (GMEL.) O. Kuntze (Menyanthaceae)

A study has been made on the prefloral, floral and postfloral biology of Nymphoides peltata (Gmel.) O. Kuntze in a former river bed of the Waal and in two concrete tanks situated in the grounds of the Catholic University of Nijmegen (The Netherlands). The structure of the flowering stem and the flowering pattern have been described. The plant grows in such a way that a continuous field of flowers is maintained over a long period of the season. In the development from flower bud to mature fruit, eight stages are distinguished. The structure of the flower is described. The flowers of Nymphoides peltata fall within category ‘B’ of the system of H. Müller who divided the entomophilous flowers in seven categories, as they are not strongly specialized to cater for the visiting of only one insect group, while the nectar is totally hidden. The u.v. pattern can be considered a specialized feature of the N. peltata flower within the genus Nymphoides, being the same as in N. geminata (R. Br.) O. Kuntze (also a yellow flowering species), as a primitive feature the heterostytyl combined with a weak incompatibility system. Nymphoides peltata is a day-flowering species, the flowers withering within one day. Features of the flower which attract anthophilois insects are: a high flower-frequency and long flowering period within the season; the yellow coloured corolla with a characteristic u.v. pattern and an average diameter of 3.54 cm; a height, on average, 3.27 cm above the water surface; and a weak, sweet odour. The existence of higher temperatures round the flower than exist in the surrounding area perhapps plays no role as an attractive features, as the difference is small. The flowers have to offer nectar (sheltered by staminodes of 0.5–0.6 cm in height, pollen and perhaps some stigmmatic exudate. Predators are attracted by the insects present. The list of flower-visiting creatures contains 44 species, of which 43 are species of Hexapoda and 1 is a species of Aranea. The possible reasons for flower-visiting of the insects and their possible role in pollination are discussed. With respect to pollination, species of Apidae, Syrphidae and Ephydridae seem to be most important. Species of Apidae and some species of Syrphidae can reachh the nectar by using their long tongues (longer than 5–6 mm). Most species of Syrphids and all Ephydrid species use pollen and liquid substances, but their tongues are too short to reach the nectar, which contains fructose and glucose in equal amounts. Apidae and Syrphidae fly from flower to flower while the Ephydridae show an irregular pattern of flower visiting; they are very important as they are present in large numbers. In contrast to the Apidae and Syrphidae, the Ephydridae also occur very commonly on the floating leaves of Nymphoides peltata. Of the 44 species mentioned, 30 species were seen only on the flowers while 14 species were also commonly found on the floating leaves. The first category is attracted most strongly by the characteristics features of the flower, while the second category is more strongly attracted to the nymphaeid system. Each flower visitor can cause pollination, and in the case of short-styled flowers also self-pollination, by which small capsules are produced with a low number of seeds (generally below 10–15). The release of developed seeds occurs 32–60 days after the day of anthesis of the flowers. Both in the field and the concrete tanks where both floral forms occur, distinct differences in the fruit and seed production were observed. The number of fruits and the number of developed seeds per m 2 was much higher in the concrete tanks due to the development of much more flowers than in the Oude Waal, but the average number of seeds per fruit was here much lower and the percentage of fruits with a number of seeds below 15, was higher which indicates that the flowers in the small isolated concrete tanks were not so efficiently pollinated as in the field, possibly because some important Ephydrid species such as Notiphila brunnipes R.-D. were not present in the concrete tanks. The seeds of Nymphoides peltata produced in the Oude Waal numbered more than 3000 per m 2, which initially floating on the water surface, and then become dispersed over the water by wind, and by water birds. When the frost period begins, nearly all seeds have sunk to the river bottom.

Intra-Inflorescence Variability in Pollen/Ovule Ratios in the Cleistogamous Species Lamium amplexicaule (Labiatae)

A comparative study was made of the various floral forms in the main shoot inflorescence of the cleistogamous species Lamium amplexicaule L. (Labiatae). This study revealed significant differences in pollen/ovule (P/O) ratios between successively produced flowers. The variation in P/O ratio is due to a change in pollen count/flower and not in ovule number. The study included two plant populations, one grown in November when only closed flowers are produced, and the other grown in April when open flower production occurs at the upper nodes. The intra-inflorescence variation in P/O ratio among the spring population showed a correlation between P/O ratio and breeding system. The cleistogamous flowers had low P/O ratios of about 200 while the chasmogamous flowers had higher P/O ratios of about 600.

INTRA‐INFLORESCENCE VARIABILITY IN POLLEN/OVULE RATIOS IN THE CLEISTOGAMOUS SPECIES LAMIUM AMPLEXICAULE (LABIATAE)

A comparative study was made of the various floral forms in the main shoot inflorescence of the cleistogamous species Lamium amplexicaule L. (Labiatae). This study revealed significant differences in pollen/ovule (P/O) ratios between successively produced flowers. The variation in P/O ratio is due to a change in pollen count/flower and not in ovule number. The study included two plant populations, one grown in November when only closed flowers are produced, and the other grown in April when open flower production occurs at the upper nodes. The intra‐inflorescence variation in P/O ratio among the spring population showed a correlation between P/O ratio and breeding system. The cleistogamous flowers had low P/O ratios of about 200 while the chasmogamous flowers had higher P/O ratios of about 600.

Dioecious Solanum species of hermaphroditic origin is an example of a broad convergence

Unlike the taxa in some genera which show a range of variability in floral morphology, species of Solanum deviate very little from the typical hermaphroditic flower. The known deviant taxa fall into two classes: most are andromonoecious (male and hermaphroditic flowers on the same plant), and the remaining few are androdioedous (male flowers on one plant, hermaphroditic flowers on another)1.I report here evidence for the first instance of a truly dioecious species of Solanum, a significant discovery in the light of the floral uniformity of this large (second only to Senecio) and economically important genus. The most closely related species and species groups comprise only hermaphroditic forms; this dioecious species is among the few non-hermaphroditic forms native to the New World, the area of greatest species diversity of the genus. Furthermore, as shown below, the species is characterised by a functionally, though not morphologically, dioecious condition. Finally, this demonstration that the two floral forms represent different sexes of the same species, rather than (as originally described) different species, impels closer analysis of other species pairs.

Heterostyly in a tropical weed: the reproductive biology of the Turnera ulmifolia complex (Turneraceae)

Turnera ulmifolia (Turneraceae) is a polymorphic complex native to the New World tropics which is composed of heterostylous and homostylous forms. The distylous varieties elegans, intermedia, and surinamensis exhibit the typical expression of heterostyly. Floral dimorphism is associated with a strong self-incompatibility system and size dimorphism of pollen. Approximately equal representation of floral morphs occurred in 24 out of 28 New World populations surveyed. In 9 out of 10 populations studied, there were no significant differences between the seed fecundity of floral forms. Populations of the homostylous variety angustifolia are self-compatible and produce monomorphic pollen.In contrast to the majority of heterostylous species, some varieties of T. ulmifolia are ruderal weeds. Varieties angustifolia, elegans, and intermedia are also used as garden ornamentals, and man has played a major role in the expansion of their ranges. Weediness in T. ulmifolia is not associated with features commonly found in other weed species, such as self-compatibility, vigorous clonal propagation, and long-distance seed dispersal. However, the continuous year-round flowering of T. ulmifolia plants gives populations a high reproductive capacity. Seed dispersal is by ants which transport seeds relatively short distances. Local seed dispersal favors the establishment of dense populations and increases the likelihood of seed set. Hence the dispersal system of T. ulmifolia appears to be coadapted with the population requirements of the breeding system.

Dispersal Patterns and the Evolution of Distyly in Oxalis alpina

Individuals from distylous and ti-istylous populations of Oxalis clpiina (Rose) Knuth (section Ionoxalis) from southeastern Arizona were crossed and the fitness of the resultant F1 hybrids analyzed to provide estimates of genetic divergence among populations. Crossability was highest when tristylous individuals were used as seed parents. Ci-osses among distylous populations resulted in the lowest seed set. Proportions of flowering F1 progeny were highest for crosses with ti-istylous individuals as seed parents, and lowest for distylous x distylous crosses. Pollen fer-tility of F1 progeny was higher in the tristylous x tristylous crosses than in distylous x distylous crosses. Results consistently indicated a higher degree of genetic relationship among tristylous populations than among distylous populations. A likely explanation for the present distribution of tristylous and distylous populations in Arizona is the initial migration of a tristylous race into this region, followed by disjunction into isolated populations due to Pleistocene drying. Following isolation, variation in evolutionary rate has apparently resulted in i-etention of tristyly in some populationis, and the independent evolution of distyly in those populations Which have diverged at the greatest r-ates. Crossability data and analysis of F1 fitness thus suggest a likely dispersal pattern for 0. alpina in southeaster-n Arizona as well as the evolutionar-y relationship between tristylous and distylous reproductive systems in this species. In southeastern Arizona, adjacent New Mexico and the Mexican states of Sonora and Chihuahua, populations of Oxalis alpina (Rose) Knuth (section Ionoxalis) occurring at forested higher elevations possess either tristylous or distylous reproductive systems. In distylous populations approximately half the individuals in the population produce flowers with long styles and short stamens, while the remaining individuals produce flowers with short styles and long stamens. Pollinations leading to fertilization and seed set are those occurring between the two forms. Selfpollinations and pollinations among individuals with identical floral form fail to result in seed set. The incompatibility relationships of distylous populations of 0. alpina are similar to those found in many distylous species occurring in other plant families. Three floral forms are found in the tristylous populations. Although the morphological features of the floral forms are similar to those found in many tristylous species, the incompatibility relationships are unusual, resembling those found in distylous populations. On the basis of these unusual incompatibility relationships, I have suggested that distyly has evolved from tristyly in this region (Weller, 1976a). Cytogeographic evidence supports the same general trend in the remaining species of section Ionoxalis (Weller and Denton, 1976). Tristylous and distylous populations of Oxalis alpina in southeastern Biological Sciences, University of Illinois. Chicago IL. 60680.

Pollination Ecology of Vernal Angiosperms

Pollination interrelationships of vernal, herbaceous angiosperms in a deciduous forest in southwestern Ohio, USA, were studied for 3 seasons with particular emphasis on phonological integration of the bionomics of flowers and the annual colonies of Bombus pollinators. Except for Corydalis flavula, all plants were insect or bird-dependent for pollination. In general, the spectrum of Bombus species on flowers was related to time of emergence from hibernation of bumblebee queens, sequence of anthesis, depth of nectariferous tubes or spurs of flowers in relation to measured proboscis lengths of bumblebee foragers, and site preference for pollinator nesting and foraging. Spectral reflectance from corollas measured spectrophotometrically indicated general correspondence of corolla color and visual spectra of pollinators. Analysis of nectars by refractometry and thin-layer chromatography revealed no preference of pollinators for particular sugars in nectar nor for particular sugar concentrations. Such preference is considered to be related to availability and abundance of nectar. As determined by analysis of corbicular pollen loads from pollinators, fidelity of bumblebee queens to specific flowers was 60%. Only 9.5% of 1457 queens investigated foraged for pollen. Close correspondence of floral form and insect behavior was indentified by means of cinematography and stereophotographic analysis of pollinator activity. Except for possible interactions between Dicentra species and Corydalis, no clear evidence for competition between pollinators for forage or between plant species for pollinators was observed. The pollination system of the vernal flora is considered to reflect a high degree of coadaptive integration of phenological, ethological, and morphological phenomena in dynamic homeostasis involving constant, but very gradual, change.

Tristyly in Eichhornia crassipes (Mart.) Solms (Water Hyacinth)

Tristyly in Eichhornia crassipes (Mart.) Solms (Water Hyacinth)

THE BREEDING SYSTEM OF PONTEDERIA ROTUNDIFOLIA L., A TRISTYLOUS SPECIES

SUMMARYPopulations of Pontederia rotundifolia in the Lower Amazon and Costa Rica are tristylous. A strong pollen trimorphism is associated with differences in stamen and style length in the three floral forms. The results of a controlled pollination programme with thirty individual plants of P. rotundifolia demonstrate that floral trimorphism is accompanied by a physiological self‐incompatibility system typical of many heterostylous plants. Legitimate pollinations are considerably more productive of seed than illegitimate pollinations. Individual plants exhibit differences in the strength of self‐incompatibility, but in general, short‐styled plants possess the strongest self‐incompatibility, long‐styled plants are intermediate and mid‐styled plants have the weakest self‐incompatibility. Large differences in the strength of self‐incompatibility are expressed in self‐pollinations with pollen from the two anther levels of each style form.Natural populations of P. rotundifolia often contain only a single style form or contain unequal proportions of style forms. Seed set, resulting from moderate self‐compatibility, occurred in a Cosra Rican population that contained only short‐styled plants. Two populations associated with rice cultivation in the Lower Amazon contained equal proportions of the three style forms. The seed set of the three forms within these populations was similar. The floral trimorphism and breeding system of P. rotundifolia are compared with those of the related P. cordata and Eichhornia crassipes.

BREEDING SYSTEM POLYMORPHISM IN A HETEROSTYLOUS SPECIES.

Heterostylous breeding systems have been the subject of continued interest since the work of Hildebrand (1866, 1871, 1887) and Darwin (1865, 1877) revealed the association of floral heteromorphism with an incompatibility system enforcing outcrossing. However, little is known of the selective factors that favor the development of heterostyly, or the selective forces which act to cause modifications of heteromorphic breeding systems. The evolutionary relationship of distyly and tristyly where they occur together in the same family has remained unclear. In Oxalis section Corniculatae, where both reproductive systems occur together, the derivation of distyly from tristyly has been suggested (Ornduff, 1972). The occurrence of distylous and tristylous populations of Oxalis alpina (section Ioenoxalis), a species of the southwestern United States, Mexico and Guatemala, suggested that studies of this species could provide further information on the evolutionary relationship of distyly and tristyly, and indicate how changes in heterostylous breeding systems have occurred. In trimorphic populations of Oxalis alpina the stigmas of one floral form occupy the lowest position in the flower, and the two sets of anthers occupy the middle and upper positions (Fig. 1). In a second floral

The Reproductive System of Amsinckia grandiflora, a Distylous Species

The flowers of Amsinckia grandiflora are distylous and the pollen is dimorphic in size. The single knozwn population of this annual species contained a 1: 1 representation of the two morphs during two seasons, but a 2: 1 pin: thrum ratio in a third season. The chief insect visitor to the flowers is Anthophora edwardsii, a bee that preferentially removes thrum pollen. Pin stigmas receive more pollen grains than thrum stigmas and also a greater proportion of illegitimate pollen than thrums. Seasonal fluctuations in the representation of the two morphs have no striking influence on pollen-flow patterns. Two sympatric, aggressive homostylous weeds of the same genus produce more seeds per flower than does A. grandiflora. It is possible that the greater reproductive success of these zweedy species has allowed them to displace A. grandiflora over much of the latter's former range. Amsinckia grandiflora Kleeberger (Boraginaceae) is an annual herb now restricted to a single, small population in San Joaquin County, California. The flowers are distylous, and the two floral forms differ conspicuously in the position of the anthers and the length of the style (Fig. 1-4). The floral morphology and highly restricted distribution of this species con- trast sharply with those of a number of other members of the genus, such as A. tessellata Gray and A. intermedia Fischer c Amsinckia is of particular interest because of the occurrence within it of distyly and an array of derived homostylous systems. In view of the con- trasts between the floral heteromorplhism and restricted distribution of A. grandiflora, a primitive species of the genus (Ray & Chisaki, 1957b), and those of its more successful homostylous congeners, I have studied the reproductive system of this species. This paper presents the results of this study and suggests that the present restricted distribution of the species is perhaps associated with its archaic and relatively inefficient reproductive system.

THE POLLINATION ECOLOGY OF PEDICULARIS (SCROPHULARIACEAE) IN THE YUKON TERRITORY

The pollination ecology of six native species of Pedicularis (Scrophulariaceae) was investigated in the Kluane Range of the St. Elias Mountains in the Yukon Territory (Canada). Seed production in all species depended upon pollination by bumblebees (Bombus Latr. spp.). Asexual propagation by root and crown branching was present in P. capitata and P. langsdorfii. Cinematographic and stereophotographic records indicated that bumblebee queens foraged in an upright (nototribic) position for nectar and pollen. Bombus workers foraged upright on P. verticillata, inverted (sternotribic) on P. labradorica, and in both positions on P. capitata, P. kanei, P. langsdorfii, and P. sudetica. The potential for hybridization between Pedicularis species by reason of overlapping blooming periods, sharing of the same or adjacent habitats, and recovery of individually marked pollinators was noted. Analysis of 1402 corbicular pollen loads from 1769 pollinating bumblebees of 14 species of Bombus on Pedicularis revealed that equal numbers of pure and mixed loads were collected. This suggested a low level of forager fidelity to a single plant species. Investigation of colors of corollas in visible light by reflectance spectrophotometry and in long‐wave (360 nm) ultraviolet light by photography revealed distinct reflectance spectra for visible light but no ultraviolet reflectance. A wide range of concentrations of sugar in nectars from the six species of Pedicularis was detected by refractometry. Chromatographic analysis of nectars indicated fructose and sucrose in nectars of four species with P. kanei and P. langsdorfii having additional glucose and raffinose or glucose and rhamnose, respectively. Nectar was abundant in all species except P. labradorica. A comparison of lengths of nectariferous tubes of corollas, lengths of tongues (prementum plus glossa) of pollinators, behavior of pollinators, and diversity of species of pollinators on each species of Pedicularis indicated that adaptive behavior of pollinators was related to the length of tongues of pollinators. It is suggested that interactions between floral mechanisms and pollinating insects probably contributed substantially to the present diversity of floral form in species of Pedicularis in North America.

Heterostyly and pollen flow in Hypericum aegypticum (Guttiferae)

Distyly in Hypericum aegypticum is associated with a moderately strong incompatibility system. Pollen size is dimorphic and pin flowers produce more pollen grains than thrum flowers. A population studied in Morocco has plants with pin flowers and those with thrum flowers present in a 1: 1 ratio. In the field, stigmas of pin flowers receive 1.5 times as many pollen grains as those of thrum flowers. At least half the pollen grains in the pollen load on stigmas of both forms are incompatible grains originating from the same floral form. Although ample compatible pollen is received by stigmas of both forms to account for a full seed set, the overall pattern of pollen flow in the species does not fit the Darwinian ideal. In Hypericum, the unique occurrence of distyly in H. aegypticum, H. aciferum and H. russeggeri, the three species comprising section Adenotrias, and the derivative nature of these species within the genus, indicate that heterostyly has evolved within the genus and is not a primitive trait.