Bumblebee pollination of Cypripedium macranthos var. rebunense (Orchidaceae); a possible case of floral mimicry of Pedicularis schistostegia (Orobanchaceae)

 Nectarless flowers of Cypripedium macranthos var. rebunense are pollinated by only queen Bombus pseudobaicalensis, which also pollinates nectar-producing flowers of Pedicularis schistostegia. Our previous study (Sugiura et al. 2001) suggested that they form a floral mimicry system: (1) Flowering phenology of both plants overlapped greatly. (2) Cypripedium occurred with lower frequency relative to Pedicularis. And (3) in a mixed stand of both plants, foraging bumblebees were sometimes confused between the mimic and model flowers. The present study clarified the system with new evidence. (4) Flower colour of Cypripedium and Pedicularis would be similar within the range of a bumblebee's visual spectrum. And (5) both species largely overlapped in spatial distribution. Based on these findings, we discuss how C. macranthos var. rebunense differs in pollination mechanism from other congeneric species, especially C. calceolus. Received April 23, 2002; accepted August 23, 2002 Published online: November 28, 2002 Addresses of the authors: Naoto Sugiura (e-mail: sugiura@aster.sci.kumamoto-u.ac.jp), Department of Environmental Science, Faculty of Science, Kumamoto University, Kumamoto 860-8555, Japan. Masashi Goubara, United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan. Kenji Kitamura, Division of Environmental Biology, Faculty of Life and Environmental Science, Shimane University, Mastue 690-8504, Japan. Ken Inoue, Biological Institute and Herbarium, Faculty of Science, Shinshu University, Matsumoto 390-8621, Japan.     

Isolation of heterothallic yeast strains ofMetschnikowia Kamienski and their mating reactions withChlamydozyma Wickerham spp

Isolation ofMetschnikowia bicuspidata var.australis in the haplophase from Antarctic waters, andM. bicuspidata var.zobellii in haplo-and diplophases at Chatham Is. N.Z., led to the study of mating reactions within theChlamydozyma - Metschnikowia complex. The results indicate the phylogenetic relationships between species. The plant-associatedCh. pulcherrima. Ch. reukaufii, andM. zygota are distinct species; when cross-mated they will conjugate but not produce asci. These three species are closely related toM. bicuspidata; when they are mated withM. bicuspidata and its varieties (var.australis and var.zobellii) asci are produced without spores. The taxonomic status ofM. bicuspidata and its varieties is based on less frequent formation of ascospores between than within taxa.The new varietyM. bicuspidata var.australis and the new combinationsM. zygota andM. bicuspidata var.zobellii are proposed.Contribution No. 925 from the Institute of Marine Sciences, University of Miami, Florida.     

Supply and partitioning of assimilates to roots of Medicago sativa L. and Lotus corniculatus L. under anoxia

Abstract A current explanation of the mechanism of flooding injury to roots suggests that oxygen deficiency depresses the supply of respirable carbohydrates sufficiently to inhibit fermentation. However, even though it has been shown that phloem transport of assimilate is sharply reduced to anaerobic roots, inhibition of assimilate metabolism has also been suggested to be an important factor. This study examines these hypotheses by relating assimilate supply and metabolic activity in anoxic roots of alfalfa (Medicago sativa L.), a flood-intolerant species, and birdsfoot trefoil (Lotus corniculatus L.), a flood-tolerant plant. Roots were made anoxic (severe O₂ deficiency) for 2, 4 or 6 d and shoots were labelled with ¹⁴CO₂. Assimilate transport to the roots and metabolism to structural components were significantly decreased in both species in response to anoxia. Trefoil exhibited significantly greater ¹⁴C incorporation into the residue fraction at 4 d anoxia than did alfalfa, and this was consistent with the greater flooding tolerance of trefoil. When assimilate supply to O₂-deficient roots was decreased by shoot shading, shoot fresh weight was reduced by both anoxia and light treatments. Root-soluble sugars were significantly decreased by shading but were greatly increased in response to anoxia. Root starch concentration also increased under anoxia. Root K⁺ concentration was reduced by anoxia only. The energy status (ATP/ADP) of roots was significantly decreased by shading; however, anoxia reduced the energy status only in unshaded plants. The data indicate that carbohydrate supply to anaerobic roots does not appear to be a limiting factor in the metabolic response of alfalfa roots. Alternatively, metabolism of assimilate in anoxic roots may be an important determinant of survival.     

Comparative lime requirements of tropical and temperate legumes

Summary In a field trial using a continuous function design, calcium carbonate was applied to a nitrogen deficient Hawaiian Oxisol at rates which increased along the plant row from 0 to 22 tons/ha, producing a gradient in soil pH from 4.7 to 7.1. Inoculated legumes representing 18 species were grown.Lime response curves showed no distinct general difference between tropical and temperate legumes. Within each group, individual species varied. Responsiveness rankings of species varied depending on criterion of response.The species ranked as follows according to the amount of lime needed for 90% of the maximum attained yield: Coronilla varia (16 tons/ha) > Leucaena leucocephala (11) > Phaseolus vulgaris, Medicago sativa (9–10) > Glycine max var. Kanrich (7) > Glycine wightii var. Cooper, Lotus corniculatus (6) > Glycine wightii var. Tinaroo, Trifolium repens, Trifolium subterraneum (5) > Desmodium canum, Dolichos axillaris, Glycine max var. Kahala (4) > Arachis hypogea, Desmodium intortum, Vigna sinensis (1–2) > Stylosanthes fruticosa, Stylosanthes guyanensis (0.1).The species ranked as follows according to the magnitude of yield increase due to lime: C. varia (20-fold increase) > T. repens (9-fold) > L. leucocephala, D. axillaris, M. sativa (6-fold) > G. wightii var. Tinaroo (5-fold) > P. vulgaris (4-fold) > G. wightii var. Cooper, L. corniculatus (3-fold) > D. canum, D. intortum, T. subterraneum (2-fold) > A. hypogea, G. max, S. fruticosa, S. guyanensis, V. sinensis (30–50%).Improved calcium availability could account for plant responses to lime rates over 3 to 4 tons/ha. Only 4 tons CaCO₃ sufficed to raise soil pH to 6 and depress solution aluminum and manganese to low concentrations, but 6 tons were needed to raise soluble calcium to 1 meq/l and 20 tons to raise it to 3 meq/l.Journal series No. 1953 of the Hawaii Agricultural Experiment Station.Department of Soils and Plant Nutrition, University of California, Davis.Department of Agronomy and Soil Science, University of Hawaii, Honolulu.     

Infectivity of Chlorella species for the ciliate Paramecium bursaria is not based on sugar residues of their cell wall components, but on their ability to localize beneath the host cell membrane after escaping from the host digestive vacuole in the early infection process

Summary. Paramecium bursaria cells harbor several hundred symbiotic algae in their cytoplasm. Algae-free cells can be reinfected with algae isolated from algae-bearing cells or cultivated Chlorella species through the digestive vacuoles. To determine the relationship between the infectivity of various Chlorella species and the nature of their cell wall components, algae-free P. bursaria cells were mixed with 15 strains of cultivated Chlorella species and observed for the establishment of endosymbiosis at 1 h and 3 weeks after mixing. Only 2 free-living algal strains, C. sorokiniana C-212 and C. kessleri C-531, were maintained in the host cells, whereas free-living C. sorokiniana C-43, C. kessleri C-208, C. vulgaris C-27, C. ellipsoidea C-87 and C-542, C. saccharophila C-183 and C-169, C. fusca var. vacuolata C-104 and C-28, C. zofingiensis C-111, and C. protothecoides C-150 and C-206 and the cultivated symbiotic Chlorella sp. strain C-201 derived from Spongilla fluviatilis could not be maintained. These infection-incapable strains could escape from the host digestive vacuole but failed to localize beneath the host cell membrane and were eventually digested. Labeling of their cell walls with Alexa Fluor 488-conjugated wheat germ agglutinin, GS-II, or concanavalin A, with or without pretreatment with 0.4 N NaOH, showed no relationship between their infectivity and the stainability with these lectins. Our results indicate that the infectivity of Chlorella species for P. bursaria is not based on the sugar residues on their cell wall and on the alkali-insoluble part of the cell wall components, but on their ability to localize just beneath the host cell membrane after escaping from the host digestive vacuole. Correspondence and reprints: Environmental Science and Engineering, Graduate School of Science and Engineering, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8512, Japan.     

Nitrogen-fixation associated with the marine blue-green alga,Trichodesmium, as measured by the acetylene-reduction technique

Summary The marine blue-green alga, Trichodesmium, was collected from the Gulf Stream, near Miami, and occurred in two distinct colonial forms both of which reduced acetylene to ethylene. Trichodesmium was more abundant during the summer but its acetylene-reducing potential showed no obvious seasonal variation. Illuminated Trichodesmium reduced acetylene to ethylene equally well either anaerobically or aerobically (20% oxygen). Acetylene-reduction in the dark, however, was oxygen-dependent and was usually 25% or less of the activity recorded in the light. 0.3–1.0 nmoles of ethylene were produced per minute per mg of protein, by illuminated cultures, and these values compare favorably with those recorded for other nitrogen-fixing blue-green algae. However, the possibility that bacteria contributed to the acetylene-reducing activity associated with Trichodesmium was not completely eliminated.Contribution No. 1578 from the University of Miami, Rosenstiel School of Marine and Atmospheric Science, 10 Rickenbacker Causeway, Miami, Florida 33149, U.S.A.     

Leucosporidium gen. n., the heterobasidiomycetous stage of several yeasts of the genusCandida

Investigation of yeasts from Antarctic regions revealed that certain species ofCandida have heterobasidiomycetous life cycles. Two distinct but overlapping groups of species were found: heterothallic and self-sporulating species.Candida scottii is a heterothallic species with the following life cycle: opposite mating types will conjugate and develop a dikaryotic mycelium with clamp connections. Karyogamy occurs in the teliospore which germinates and produces a promycelium. Meiosis takes place in the promycelium, followed by development of haploid sporidia to complete the life cycle. In addition,C. scottii has a self-sporulating phase. From a single cell, in the apparent absence of mating, a uninucleate mycelium is produced that lacks clamp connections. Teliospores, promycelia and sporidia develop that appear similar to those produced from dikaryotic mycelium.The self-sporulating species have life histories similar to the self-sporulating phase ofC. scottii; except that heterothallism has not been observed.Based on these life histories the new genusLeucosporidium is proposed with two heterothallic species (Leu. scottii andLeu. capsuligenum) and five self-sporulating species (Leu. antarcticum, Leu. frigidum, Leu. gelidum, Leu. nivalis andLeu. stokesii. Leu. antarcticum) andLeu. stokesii have not been described under the genusCandida.Contribution No. 1138 from the Institute of Marine Sciences, University of Miami, Fla.This study was supported by the National Science Foundation through the Office of Antarctic Programs, Grant GA-3957. The authors are grateful to Dr. E. Marelli for editing the Latin diagnosis.     

Isolation and characterization of microsatellite loci from the Blanding’s turtle,Emydoidea blandingii

Independent microsatellite development efforts at the University of Miami and Dalhousie University resulted in seven microsatellite loci for the Blanding’s turtle (Emydoidea blandingii). The level of polymorphism ranged from three to 15 alleles with observed heterozygosities ranging from 0.31 to 0.95. Cross species amplification suggests that these loci may have utility in other turtle species.     

Effect of temperature on potassium and calcium transport from within the root to the xylem exudate of tobacco

Summary Detopped root systems of tobacco plants (Nicotiana tabacum L. var. Virginia Gold) were exposed to air at different temperatures (14 to 23°C). The volume of xylem exudate was related to temperature and decreasing the temperature resulted in a lag in the appearance of exudate. For 4 and 8 days of exudation the amounts of cations transported in the exudate were temperature dependent. The Q₁₀ values were higher than usually encountered in biological reactions; the mean value was around 6. This work was supported in part by National Science Foundation Grant GB8170. University of California     

HYBRIDIZATION STUDIES WITH SPECIES OF CYNODON FROM EAST AFRICA AND MALAGASY

A collection of 198 accessions of Cynodon from East Africa and Malagasy was grown in uniform nurseries at Stillwater, Okla., and classified morphologically, studied cytologically, and tested for crossability in hybridization studies. The following taxa were recognized: C. arcuatus, C. plectostachyus, C. aethiopicus, C. nlemfuensis var. nlemfuensis, C. nlemfuensis var. robustas, C. dactylon var. aridus, C. dactylon var. coursii, and C. dactylon var. dactylon. The magnitude of barriers to gene flow was estimated by ease of hybridization and by sterility of the hybrids obtained. C. arcuatus and C. plectostachyus are well isolated from all other species in the genus. The others are sufficiently related that they may be intercrossed. The barriers to gene flow vary demonstrably in strength between different combinations of taxa. The magnitude of a barrier required to establish species limits is, perhaps, more a matter of subjective opinion than a scientific conclusion. It was concluded that no completely satisfactory classification of the genus is possible. The system adopted was a compromise between classical morphological concepts of species, the biological concept of species, and pragmatic utility.     

Yeast species utilizing uric acid,adenine,n-alkylamines or diamines as sole source of carbon and energy

Yeast strains utilizing uric acid, adenine, monoamines or diamines as sole source of carbon and energy were isolated from several soil samples by the enrichment culture method. The most common species wasTrichosporon cutaneum. Strains ofCandida catenulata, C. famata, C. parapsilosis, C. rugosa, Cryptococcus laurentii, Stephanoascus ciferrii andTr. adeninovorans were also isolated. All strains utilizing uric acid as sole carbon source utilized some primaryn-alkyl-l-amines hydroxyamines or diamines as well. The ascomycetous yeast strains showing these characteristics all belonged to species known to assimilate hydrocarbons. Type strains of hydrocarbon-positive yeast species which were not found in the enrichment cultures generally assimilated putrescine, some type strains also butylamine or pentylamine, but none assimilated uric acid. Methanol-positive species were not isolated. Type strains of methanol-positive and of hydrocarbon-negative species did not assimilate uric acid, butylamine or putrescine. Assimilation of putrescine as sole source of carbon and energy may be a valuable diagnostic criterion in yeast taxonomy.     

Lack of Ecotypic Differentiation: Plant Response to Elevation,Population Origin,and Wind in the Luquillo Mountains,Puerto Rico1

How important is ecotypic differentiation along elevational gradients in the tropics? Reciprocal transplants of two shrubs, Clibadium erosum (Asteraceae) and Psychotria berteriana (Rubiaceae), and a palm, Preitoea acuminata var. montana (Palmaceae), were used to test for the effect of environment and population origin on growth and physiology in the Luquillo Experimental Forest of Puerto Rico. Two sites were used, one at Pico del Este (1000 m in cloud forest) and one at El Verde (350 m in lower montane rain forest). At the cloud forest site, plastic barriers were erected around a subset of the plants to examine if protection from wind affected survival or biomass accumulation. Survival of C. erosum and P. berteriana was not affected by site, population origin, or the presence of barriers. For P. acuminata var. montana, survival was higher for plants with barriers, but not affected by site and population origin. Plants of C. erosum and P. berteriana at El Verde grew larger than at Pico del Este, but there was no effect of population origin or barrier treatment on biomass accumulation for these species. For P. acuminata var. montana, there was no effect of environment, population origin, or barrier treatment on biomass accumulation. Light‐saturated photosynthetic rate (A_max) of C. erosum, P. berteriana, and P. acuminata var. montana, as well as leaf anatomical characteristics of C. erosum, were unaffected by environment, population origin, and barrier treatment. On balance, there seems to be little evidence of ecotypic differentiation in these species along the gradient.     

Effects of plant species and soil history on root morphology,arbuscular mycorrhizal colonization of roots,and biomass in four tallgrass prairie species

Although dominant C₄ grasses in tallgrass prairie are highly mycotrophic, for many non-dominant species neither extent of mycorrhizal colonization nor root morphology effects on plant–soil feedback interactions are known. In a laboratory study conducted from November 2013 to February 2014 at Governors State University (University Park, IL), we grew plants of a dominant C₄ grass (Andropogon gerardii) and three non-dominant forbs (Symphyotrichum laeve var. laeve, Symphyotrichum novae-angliae and Parthenium integrifolium) individually in soil collected in the field beneath a conspecific, collected beneath another study species, or in sterilized soil. The study addressed the following questions: (1) Is extent of mycorrhizal colonization of roots related to root structure? (2) How does soil history interact with plant root traits to influence plant–soil feedback? (3) How might plant–soil feedback patterns influence competitive interactions among study species? We found that proportion arbuscular mycorrhizal fungi (AMF) colonization decreased with increasing specific root length. Soil history had a stronger influence than plant species on total biomass of plants, with all species having highest total biomass when grown in Andropogon soil. Consequently, net, or heterospecific, feedback did not differ among pairwise species combinations, and was not different from 0. While these results suggest that no study species should have a competitive advantage in the field, Andropogon might still have an advantage through mechanisms such as competition for light. Future work in the field and including less mycotrophic species is needed to better understand AMF effects on competitive interactions.

     

Influence of lime on nitrogen fixation by tropical and temperate legumes

Summary A nitrogen deficient Oxisol which had been fertilized with P, K, Zn and Mo received CaCO₃ at rates which increased continuously from zero to 22 tons/ha. Liming produced a range of pH in the saturation paste from 4.7 to 7.1; a range of calcium in the saturation extract from 0.3 to 3 meq/l; and a significant decline in available manganese. Responses of 9 tropical and 7 temperate legumes were compared across the pH variable.For Stylosanthes spp. nodule numbers and weight and plant yield declined above pH 5.5. Arachis hypogaea and Vigna sinensis, whose yield increased by only 30%, showed no clear improvement in nodulation or nodule effectiveness (acetylene reduction rate per unit nodule weight).Increased nodule effectiveness could account for most of the growth increase in Dolichos axillaris and Glycine max var. Kahala. Both the number and effectiveness of nodules increased for Desmodium intortum, Glycine wightii, Medicago sativa, and Trifolium subterraneum. Nodule size and effectiveness increased for G. max var. Kanrich. Only in one species, Coronilla varia, could increase in nodule numbers alone account for the increased growth associated with liming, although increased numbers of nodules probably accounted for much of the response by Lotus corniculatus, and by Desmodium canum and D. intortum up to pH 5.3.Increased nodulation and plant N contents were consistent with the conclusion that for most species improved N₂-fixation was the cause of growth improvement associated with liming. However, percent N was high in leaves of Vigna and Phaseolus vulgaris at all lime levels. In Phaseolus, variation in nodulation and growth were unrelated. The growth improvement was associated with decline in leaf N, suggesting that something other than N nutrition was limiting.Journal Series No. 1957 of the Hawaii Agricultural Experiment Station.Department of Soils and Plant Nutrition, University of California, Davis.Department of Agronomy and Soil Science, University of Hawaii, Honolulu, Hawaii.     

Sympodiomyces gen. n., a yeast-like organism from southern marine waters

Sympodiomyces gen. n. is described with the single speciesSympodiomyces parvus sp. n. The distinguishing characteristic of this yeast-like genus is the method of asexual reproduction: conidia are produced on a conidiophore that develops sympodially. A sexual stage has not been observed, therefore the genus is placed among the Fungi Imperfecti, family Cryptococcaceae.Contribution No. 1364 from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida.The authors gratefully acknowledge Dr. Jan Kohlmeyer, Univ. of North Carolina, Morehead City, North Carolina; Dr. R. T. Moore, North Carolina State Univ. at Raleigh; Dr. H. J. Phaff, Univ. of California at Davis; Miss W. Ch. Slooff and Mr. D. Yarrow, CBS, Delft, Netherlands; Dr. K.Tubaki, Institute for Fermentation, Osaka, Japan; and Dr. J. A. von Arx, C.B.S., Baarn, for examining cultures ofS. parvus. Dr. D. P. Rogers, Univ. of Illinois, Urbana, Ill, prepared the generic Latin diagnosis. Mr. Steven Y. Newell and Mr. A. Weiner, Univ. of Miami, assisted in obtainingEltanin collections. This study was supported by the National Science Foundation through the Office of Antarctic Programs Grant No. GA 13675.     

The relationship of diet to growth and ammonium excretion in salt marsh fish

Synopsis Detritus is an abundant but poor quality food source for consumers in salt marsh ecosystems. Here we present results of feeding experiments to determine the ability of Fundulus heteroclitus, Cyprinodon variegatus, and Mugil cephalus, three major detritivores in Great Sippewissett Marsh, Massachussetts, to assimilate detritus and use it for growth. C. variegatus, the sheepshead minnow, gained weight on a detrital diet, but F. heteroclitus, the marsh killifish, and juvenile M. cephalus, the striped mullet, lost weight and suffered high mortality on detrital diets. C. variegatus is a herbivore with morphological adaptations for ingesting plant material. F. heteroclitus is a carnivore poorly suited to effectively assimilate detritus from the diet. Although adult M. cephalus are adapted for ingesting and assimilating detrital material, the young may lack these adaptations and thus do not assimilate detritus. C. variegatus excretes ammonium at a lower rate than F. heteroclitus when fed animal food, or when starved for short periods of time. This protein sparing effect could be crucial for survival when detritus is the only food available at certain times of the year. While both C. variegatus and M. cephalus are visitors in the marsh and may leave to exploit food sources elsewhere, F. heteroclitus is a year-round resident and is the most abundant species of fish in the marsh. Yet when high quality food sources become scarce in late summer and fall, detritus, although plentiful, is apparently not a suitable alternative.To whom all correspondences should be addressed.     

Taxonomic position of a Chinese <Emphasis Type="Italic">Pleurotus</Emphasis> “Bai-Ling-Gu”: it belongs to <Emphasis Type="Italic">Pleurotus eryngii</Emphasis> (DC.: Fr.) Quél. and evolved independently in China

The Chinese Bai-Ling-Gu is a mushroom named Pleurotus eryngii var. tuoliensis C.J. Mou. This species has been identified as P. nebrodensis or P. eryngii var. nebrodensis. We examined its taxonomic position by analysis of mating, cultivation, and rDNA sequences, and concluded as follows. (1) Bai-Ling-Gu mated with P. eryngii var. eryngii, and the F₁ and F₂ formed fruit bodies. (2) Bai-Ling-Gu mated with P. eryngii var. ferulae, and the F₁ formed fruit bodies. (3) In the di-mon mating test, P. eryngii var. nebrodensis from Sicily mated with monokaryons of P. eryngii var. eryngii but mated hardly at all with those of Bai-Ling-Gu and P. eryngii var. ferulae. The di-mon mating pattern of Bai-Ling-Gu resembled those of P. eryngii var. ferulae. (4) The partial sequences of rDNA ITS1 and IGS1 from the epitype of P. nebrodensis were identical with those from P. eryngii var. nebrodensis from Sicily but differed from those from Bai-Ling-Gu. (5) The strains of P. eryngii var. eryngii and P. eryngii var. ferulae were in a group, the strains of P. eryngii var. nebrodensis from Sicily were in another group, and the strains of Bai-Ling-Gu were in the other group in both the phylogenetic trees based on the ITS1 and the IGS1 sequences. These results led to the conclusion that Bai-Ling-Gu is a variety of P. eryngii and evolved independently in China. It is satisfactory to identify Bai-Ling-Gu with P. eryngii var. tuoliensis C.J. Mou.     

Airborne‐pollen pool and mating pattern in a hybrid zone between Pinus pumila and P. parviflora var. pentaphylla

The reproductive isolation barriers and the mating patterns among Pinus pumila, P. parviflora var. pentaphylla and their hybrids were examined by flowering phenology and genetic assays of three life stages: airborne‐pollen grains, adults and seeds, in a hybrid zone on Mount Apoi, Hokkaido, Japan. Chloroplast DNA composition of the airborne‐pollen was determined by single‐pollen polymerase chain reaction. Mating patterns were analysed by estimating the molecular hybrid index of the seed parent, their seed embryos and pollen parents. The observation of flowering phenology showed that the flowering of P. pumila precedes that of P. parviflora var. pentaphylla by about 6 to 10 days within the same altitudinal ranges. Although this prezygotic isolation barrier is effective, the genetic assay of airborne‐pollen showed that the two pine species, particularly P. pumila, still have chances to form F₁ hybrid seeds. Both parental species showed a strong assortative mating pattern; F₁ seeds were found in only 1.4% of seeds from P. pumila mother trees and not at all in P. parviflora var. pentaphylla. The assortative mating was concluded as the combined result of flowering time differentiation and cross‐incompatibility. In contrast to the parental species, hybrids were fertilized evenly by the two parental species and themselves. The breakdown of prezygotic barriers (intermediate flowering phenology) and cross‐incompatibility may account for the unselective mating. It is suggested that introgression is ongoing on Mount Apoi through backcrossing between hybrids and parental species, despite strong isolation barriers between the parental species.     

Effect of storage time,site and floral morph on seed germination of the threatened distylous primrose Primula cusickiana var. maguirei

Ex situ conservation of rare plant species requires an understanding of germination requirements. We report the first successful germination trials for Maguire primrose (Primula cusickiana var. maguirei[L.O. Williams] N.H. Holmgren & S. Kelso), a threatened perennial herb narrowly restricted to a 20‐km canyon in northern Utah, USA. Seeds collected from different sites (upper or lower canyon populations) and flower morphs (pin or thrum) that had been stored for either 1 or 2 years were cold, moist stratified in darkness at 1–2°C for 270 days. Independent of treatment, time to first germination was approximately 75 days, time to 50% germination (T₅₀) was approximately 165 days, and total germination was 55.8%. Higher mean germination was observed in seeds stored for 2 years compared with seeds stored for 1 year, as well as in seeds from pin flowers compared with thrum flowers. There was not a significant effect of site on mean germination, but there was a significant storage time × site interaction. Seeds stored for 2 years also had a lower mean T₅₀ versus seeds stored for 1 year. In addition, seeds from upper canyon populations had a higher mean T₅₀ than those from lower canyon populations. Our results suggest that short‐term storage should not significantly decrease seed viability, and that both flower morph and canyon location may influence germination. Evidence suggests that germination patterns are adaptive. Our results contribute to our understanding of the germination biology of P. cusickiana var. maguirei and inform future conservation efforts for this threatened species.     

Species-specific ability ofChlorella strains (Chlorophyceae) to form stable symbioses withHydra viridis

46 strains ofChlorella, identified by physiological and biochemical characters, were examined for their ability to form stable symbioses with aposymbioticHydra viridis. It was found to be a species-specific characteristic. Among the 15 taxa studied, onlyC. saccharophila var.ellipsoidea, C. saccharophila var.saccharophila, C. fusca var.vacuolata, C. kessleri, C. luteoviridis, andC. protothecoides formed stable symbioses withHydra viridis. Among the 11 known physiological and biochemical characters of theseChlorella species, only acid tolerance seems to be correlated with symbiosis: All symbiotic species are capable of growing at or below pH 4.0.