摘要:

The objective of this research was to compare the responses to increasing density of different natural populations ofDanthonia caespitosa,a perennial grass of southern Australia, under different temperature regimes. Seeds were collected from four populations along a 167‐km N–S transect beginning north of Deniliquin, N.S.W., and ending near Heathcote, Victoria. Seedlings from each population were planted in loamy sand at three densities and grown under day/night temperature regimes of 15/10, 24/19, and 33/28 C in the Canberra Ceres Phytotron. Results indicate that one natural population (or one temperature regime) can not be used to characterize this species' responses to increasing density. The effects of density and temperature on tillering, plant height, leaf length, and leaf width varied significantly among populations, so that populations achieved comparable shoot weights by different relative responses to density. Variability in biomass among individuals (as indicated by coefficients of variation) increased from low to intermediate density; however, size variability at the highest density was either greater, lesser, or approximately the same as that of plants at the intermediate density, depending upon the population and the temperature regime. The combinations of density and temperature which produced the maximum shoot growth per pot varied markedly among populations; at 24/19 C, populations from frequently disturbed areas of low perennial plant cover had greater shoot weights per pot at the intermediate density, while those populations from more stable grassland sites had their greatest shoot weights at the highest density. Flowering occurred in all populations at the low density in 15/10 C; however, only for the population from the ungrazed grassland was there any flowering in the other temperature regimes or at higher densities. It is concluded that a “response to density stress” could be differentially described for each population at each temperature regime, even though the four study populations represented only 1/10 of the latitudinal range ofD. caespitosa.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10845.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Chromosome number determinations from 360 individuals of 73 species, varieties and hybrids ofAster(not includingVirgulusRaf.) are reported for the first time. Most reports confirm one or more earlier ones for the taxa. Several first counts are included:A. curtisiiT.&G., 2n= 32;A. drummondiiLindl. var.drummondii,2n= 16;A. eulaeShinners, 2n= 48;A. infirmusMichx., 2n= 18;A. lateriflorus(L.) Britt., 2n= 64;A. meritusA. Nels., 2n= 36;A. parviceps(Burg.) Macken.&Bush, 2n= 32;A. pubentiorCronq., 2n= 18; andA. sagittifoliusWedem., 2n= 48. Counts of 2n= 18 forA. avitusAlex. andA. hemisphaericusAlex. and 2n= 36 forA. paludosusAit. provide additional evidence that the base number ofA.sect.Heleastrumisx= 9, notx= 5. Counts of 2n = 32 and 2n= 48 forA. curtisiisupport its placement with otherx= 8 species in sect.Foliacei,but not withx= 9 species in sect.Spectabiles.The geographic distributions of cytotypes support the taxonomic delimitationsA. puniceusL. andA. praealtusPoir. Diploids were found throughout the range ofA. puniceus,but tetraploids were rare and found only in the southwestern portion of the range; ploidy level did not correlate with morphological variation. InA. praealtusthe distribution of tetraploids and octoploids correlated with the allopatric varitiespraealtusandangustiorWieg. Satellite chromosome morphology was determined in species not studied before.Aster engelmannii, A. glaucodes, A. infirmus, A. modestus, A. oregonensis, A. pauciflorusandA. pubentiorhad subequal satellites and short arms, the “primitive” type in the genus.Aster meritus, A. radulaandA. radulinahad the “derived,” subg.Astertype, a very large satellite attached to a very short proximal portion of the short arm.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10846.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Two closely related North American orchid species,Isotria verticillataandI. medeoloides,were studied with respect to breeding system biology and pollination dynamics. Marked differences in reproductive biology were revealed. The more commonI. verticillatais xenogamous, being pollinated by solitary bees in the Andrenidae, Anthophoridae, and Halictidae. The inflorescence is fragrant, multicolored, and has pollination guides, thus possessing an obvious attractant system, even though it lacks nectaries. In contrast,I. medeoloidesis self‐pollinating, has light green flowers, and lacks pollination guides, nectaries, and odor. These two species also differ radically in population structure and reproductive efficiency.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10847.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Clarkia nitensandClarkia speciosa polyantha(Onagraceae) are distinct chromosomal taxa differing by at least six reciprocal translocations. Where the taxa have come into contact, a chromosome boundary zone exists characterized by high levels of translocation heterozygosity due to at least 12 new chromosome arrangements which have evolved there. Previous studies have shown that these boundary arrangements are distributed such that they provide for full interfertility between adjacent populations. It was hypothesized that the geographic distributions of each of these arrangements will remain generally stable due largely to the very adverse effect that major changes would have on fertility. Evidence is presented here that over a ten year period the frequencies and geographic distributions of the chromosome arrangements within this boundary region have remained stable. The frequencies of the various chromosomal configurations (nine pairs, ring of four, two rings of four, ring of six, ring of four + ring of six, and ring of eight) from surveys in 1968 and 1978 have been analyzed statistically. In general, the analysis indicates that there have been no detectable changes over the 10‐yr period.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10848.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Trillium ovatum(Liliaceae) is myrmecochorous: its seeds bear large elaiosomes that are attractive to ants. Nevertheless, in coastal second‐growth redwood forests of northern California, most seedlings occur in mixed‐age clusters close to potential parents, suggesting that seed dispersal is limited. Ants were absent or rare at two relatively cool, moist study sites. At these sites, most seeds either eventually fell passively from fruits or were knocked to the ground by banana slugs that foraged on the elaiosomes. At two warmer, drier sites, a single species of ant,Lasius pallitarsis,dispersed the seeds but tended to remove the elaiosomes before returning to the nest. Thus at all sites a large number of seeds remained close to adults, accounting for the observed pattern of seedling distribution. The dispersal adaptations ofT. ovatumand other redwood forest myrmecochores probably evolved in forests where seed‐carrying ants were more common.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10849.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

This study describes nectar production patterns forIpomopsis aggregataand discusses their potential adaptive and ecological significance. It also examines the influence of environmental and other factors on nectar production rate (NPR) and nectar sugar concentration. ForI. aggregatathere were no NPR differences with flower age. An hypothesis for the presence or absence of such differences is discussed.Ipomopsis aggregatahas a relatively constant rate of nectar production during the day and production continues overnight but at a reduced rate. Newly opened flowers already have a sizeable accumulation of nectar. 24‐hr nectar sugar production on overcast days was 62% of sunny day production. NPR values at the beginning of the flowering season were almost twice as great as those near the end but the sugar concentration did not change. Whether nectar was removed periodically (to simulate pollinator visits) or simply allowed to accumulate over 24 hr had no effect on total production. Nectar sugar concentration has a characteristic diurnal pattern: highest in the afternoon and lowest in the early morning, probably in response to diurnal changes in relative humidity. Sugar concentration was also lower on overcast days. These changes are not due to evaporative losses from the open end of the flower. However, evaporation did occur in flowers which had been punctured at the base of the corolla by nectar robbing bees. In general, the results of this study suggest caution in characterizing the NPR or sugar concentration of a species by making measurements at one point in time under one set of environmental conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10850.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Observations of meiotic and/or mitotic chromosomes for 16 specific, infraspecific, and hybrid taxa from 56 populations are presented; chromosome numbers for 11 taxa are reported for the first time. All samples reported have 2n= 22, with the exception that 3 of 12 collections of C. ×intermediahave at least some individuals that are triploid. North American diploid collections of this hybrid are heterozygous for one reciprocal translocation; only 1 of 5 European diploid collections also exhibited a translocation. Meiosis in four naturally occurring Asian hybrids is also analyzed:C.×ovata(C. cordata×C. mollis),C.×decipiens(C. erubescens×C. lutetiana) andC.x×dubia(C. cordata× C.eurbescens) possess a single translocation;C.×mentiens(C. alpina×C. eurbescens) is structurally homozygous. With the exception of the translocation, chromosome pairing in these hybrids is normal. Early diakinesis chromosomes possess densely staining centric regions and diffusely staining arms that are subequal in length.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10851.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The problematic organism,Sporocarpon,was among the first fossil fungi to be described. The genus was actually a heterogeneous assemblage of fungal forms, and was eventually divided into several taxa includingSporocarpon, Dubiocarpon,andMycocarpon.In the present paper these organisms, as well as a similar, previously undescribed genus,Coleocarpon;are described from Lower, Middle, and Upper Pennsylvanian strata in North America, and from Upper Carboniferous sediments in England. Although initially considered to be radiolarian‐like protozoa, these structures show far more similarity to ascomycetous cleistothecia. All forms are ornamented, spherical bodies with a complex wall which encloses scattered asci and ascospores. Taxa are distinguished primarily by differences in the organization of the cleistothecial wall. Structurally similar organisms are found today among the Eurotiales.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10852.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

An individual ofCollomia grandifloratypically produces both closed or cleistogamous (CL) and open or chasmogamous (CH) flowers. The developmental origin of these dimorphic floral types within a plant was investigated using histological techniques, allometric relationships, and scanning electron microscopy. Prior to archesporal cell stage in the anthers, CL and CH meristems are indistinguishable. In the CL anther, an absence of ventral locule cell differentiation together with a shorter period of time between archesporial cell differentiation and meiosis in the two dorsal locules results in accelerated anther dehiscence and a smaller mature anther size and pollen grain number. Divergence between the CL and CH patterns of corolla development is coincident with microspore mitosis in the CH anther. At this point, there is an increase in growth in corolla length relative to growth in calyx length in the CH flower which does not occur in the CL flower. Calyx and ovary development are similar in the two floral forms; however, ovary expansion due to fertilization occurs earlier in the CL flower as a result of precocious anther development and stigma receptivity. The hypothesis that anther differentiation may trigger organ growth rate changes and differentiation events in the flower and hypothetical roles for abscisic acid and gibberellin in modifying floral development inC. grandifloraare discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10853.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Early spring shoot and fine‐root development of four evergreen and three deciduous shrub species were analyzed in a subarctic muskeg at Fairbanks, Alaska. The overwintered foliage of the evergreen shrubs regreened earlier than new leaves developed on the deciduous species. Likewise, the evergreen shrubs produced new fine roots earlier than the deciduous species. The total nonstructural carbohydrate (TNC) concentration did not decline in the evergreen shrubLedum palustreduring the spring development. This contrasted with the deciduous shrubBetula glandulosa,where a significant TNC reduction in stem tissue coincided with bud break and fine‐root growth flush.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb10854.x

出版商:Wiley    

年代:1983

数据来源: WILEY