摘要:

The differential germination responses of ray and disc achenes ofHemizonia increscens(Asteraceae) were compared in field and laboratory investigations in order to gain insight into the ecological and evolutionary significance of heterocarpy.In the field, 200 ray and 200 disc achenes were placed in native, sterilized soil in a series of cleared, randomized, replicated plots. In a nearby plot a similar number of achenes were placed in plastic petri dishes in which high moisture conditions were maintained. Disc achene germination occurred under relatively minimal moisture conditions (<1 cm rainfall for 19 days) and relatively mild temperature regimes (21–7 C). Disc achene germination began three days after planting in the field plot and four days after they were put into the field petri dishes. In contrast, the onset of ray achene germination occurred 21 days after planting in the field plot and 19 days after planting in the field petri dishes. Averages of 2.05 and 2.71 disc achenes/day germinated in the field plot and field petri dishes, respectively. These contrasted with averages of 0.57 and 0.50 ray achenes/day germinated in the field plot and in the field petri dishes, respectively. A total of 67.5% and 69% disc achenes germinated in the field plot and the field petri dishes, but only 18% and 16.5% ray achenes germinated in the field plot and field petri dishes, respectively.Three separate treatments, using 100 ray and 100 disc achenes in each, were performed in laboratory growth chambers: 1) nicking the fruit coat, 2) excising the embryo, and 3) leaving the fruit coat intact. Onset of germination for all disc achene treatments occurred after three days. No significant differences were found among the three disc achene treatments in timing, rate, or germination percentage. All three disc treatments in the laboratory closely paralleled those for disc achenes in the field plots in time and germination percentage, but rates of germination were not as high. Germination of the nicked and excised ray achenes treatments began after four days, while germination of the untreated ray achenes began after 27 days. Untreated ray achenes in the laboratory paralleled the ray achenes in both field experiments in rate and germination percentage, but were delayed in time of germination. The nicked and excised ray achene treatments, however, were similar to the disc achene treatments in time of germination, and were not significantly different from disc achenes in rate of germination. These data suggest 1) that ray and disc achenes are markedly different in germination under identical conditions in field and laboratory experiments, and 2) this difference in germination response may be due to the thicker pericarp of the ray achenes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08612.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

In mature flowers of the southern Andean parasitic herb,Quinchamalium chilense(Santalaceae), the stigmas and anthers are closer together in the pin morph than in the thrum morph. While the stigmas and anthers of the two morphs are in reciprocal positions as the flowers open, such reciprocity is lost as the result of post‐anthesis allometric growth of the styles and stamens. Experimental pollinations reveal that both morphs ofQ. chilenseare self‐compatible. Natural fruit set is higher on the pin morph. The latter is also statistically under‐represented in natural populations with respect to a 1:1 ratio for pins and thrums. Pin flowers produce larger numbers of pollen grains than thrum flowers and pollen of pin flowers is smaller in size than that of thrum flowers. Higher fruit set on the pin morph is consistent with some tendency towards subdioecious breeding behavior, although an expected excess of geitonogamous pollinations on the pin morph might also be contributing to the difference in fruit set on the two morphs. The unusual floral morphology ofQ. chilensecould have evolved as a result of selection for larger flowers by certain pollinator groups less likely to effect geitonogamous pollination. Alternatively, extended development of post‐anthesis flowers might be a reflection of selection for an array of flower sizes on individual inflorescences, producing a target effect for pollinator attraction. The evolution of such inflorescence morphology would have been facilitated by the fact that a trend in the direction of subdioecious breeding behavior accrues the same outcrossing advantages as strict distyly. Precise information on periods of stigma receptivity is required to further our understanding of the floral morphology ofQ. chilense.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08613.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

We used Nomarski differential interference contrast microscopy of cleared, whole ovules to examine megasporogenesis and megagametogenesis in tetraploid (N= 34) individuals of three species ofAmelanchierin Maine.Amelanchier canadensisandA. stoloniferaconform to the general pattern of apomixis in the Maloideae by being aposporous and by frequently forming more than one megagametophyte per megasporangium. These species are also pseudogamous; both self and foreign pollen elicit fruit set.Amelanchier bartramianafollows a sexual pattern by producing a triad of megaspores and almost always only one megagametophyte per megasporangium. This boreal shrub, strikingly distinct morphologically and in its habitat preference from other North American species of the genus, is primitive in its sexuality and self‐incompatibility relative to other species we have studied.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08614.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The patterns and rates of organelle redistribution in columella (i.e., putative statocyte) cells of agravitropicagtmutants ofZea maysare not significantly different from those of columella cells in graviresponsive roots. Graviresponsive roots ofZ. maysare characterized by a strongly polar movement of45Ca2+across the root tip from the upper to the lower side. Horizontally‐oriented roots ofagtmutants exhibit only a minimal polar transport of45Ca2+. Exogenously‐induced asymmetries of Ca result in curvature ofagtroots toward the Ca source. A similar curvature can be induced by a Ca asymmetry in normally nongraviresponsive (i.e., lateral) roots ofPhaseolus vulgaris.Similarly, root curvature can be induced by placing the roots perpendicular to an electric field. This electrotropism increases with 1) currents between 8–35 mA, and 2) time between 1–9 hr when the current is constant. Electrotropism is reduced significantly by treating roots with triiodobenzoic acid (TIBA), an inhibitor of auxin transport. These results suggest that 1) if graviperception occurs via the sedimentation of amyloplasts in columella cells, then nongraviresponsive roots apparently sense gravity as do graviresponsive roots, 2) exogenously‐induced asymmetries of a gravitropic effector (i.e., Ca) can induce curvature of normally nongraviresponsive roots, 3) the gravity‐induced downward movement of exogenously‐applied45Ca2+across tips of graviresponsive roots does not occur in nongraviresponsive roots, 4) placing roots in an electrical field (i.e., one favoring the movement of ions such as Ca2+) induces root curvature, and 5) electrically‐induced curvature is apparently dependent on auxin transport. These results are discussed relative to a model to account for the lack of graviresponsiveness by these roots.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08615.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The silica‐scaled algae (Synuraceae, Chrysophyceaesensu lato)are compared to other Chrysophyceae, Phaeophyceae and Bacillariophyceae with occasional comparisons to other chlorophyll c‐containing algae, scaled protozoa and oomycete fungi. The silica‐scaled algae have several unique characters which separate them from the above groups and based upon these differences a new order, Synuralesord. nov., and a new class, Synurophyceaeclass. nov., are described. The major distinguishing characters of the Synurophyceaeclass. nov.are: they have chlorophyllsaandc1but lack chlorophyllc2; their flagellar apparatus includes a microtubular root that loops around two parallel flagella and a flagellar root system which occurs in four absolute orientations; the photoreceptor consists of paired flagellar swellings which are not associated with the cell membrane and chloroplast; no eyespot is present; the nuclear envelope is not or is only weakly associated with the chloroplast endoplasmic reticulum. The Synurophyceaeclass. nov.are about equally distinct from the Chrysophyceaesensu stricto, Phaeophyceae and Bacillariophyceae when the class level characters are compared. Although the Phaeophyceae have a long history of being placed by themselves in the division Phaeophyta, and the Bacillariophyceae and Chrysophyceae have recently been placed alone in the Bacillariophyta and Chrysophyta, respectively, the similarities found among these classes suggest these algae are not so distinct that they require separate divisions. Tentatively, therefore, the Synurophyceae are placed in the division Phaeophyta along with the Bacillariophyceae and Chrysophyceaesensu stricto.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08616.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The gametophytes ofPhanerosorus majorcollected from wild populations in Seram Island are described. Young gametophytes are slender, ribbon‐like and uniformly one cell thick. They develop to old gametophytes with a broad thick cushion and coarsely ruffled wings. The gametophytes are monoecious and protandrous, although archegonia‐bearing thalli occasionally become antheridia‐bearing. Massive antheridia form on the ventral surface of young and old gametophytes while archegonia are borne on the cushion of old ones. Both young and old gametophytes reproduce vegetatively. The gametophytic characters are compared with those ofMatonia.The life cycle ofP.majoris discussed with reference to its ecology.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08617.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Depletion during spring germination (turnover), longevity, and successional relationships were studied at High Marsh (HM), Cattail (CT), and Shrub Forest (SF) sites in a freshwater tidal wetland over three years. There was significant seasonal reduction in size and composition of seed banks from all sites. Turnover was greatest in HM surface (0–2 cm) samples where 29 x more seeds germinated in March than in June. In CT and SF samples turnover was considerably less. Magnitude (34–97%) was related to species composition and factors affecting field germination. Decrease in density with depth (0–10 cm) was log‐linear in March samples. Except for SF 30–32 cm, few seeds and species were found at 8–10, 15–17, or 30–32 cm. Three seed bank strategies were distinguished: (a) complete turnover (Type II,sensuThompson and Grime 1979), (b) high turnover with some reserve (Type III), and (c) large long‐term seed reserve (Type IV). Longevity of many species appeared to be restricted; 31–56% at each site were present only in surface samples, and 29–52% germinated only in March samples. Although some species were important at all three sites, the seed bank composition of each was distinct, and was related to vegetation composition at each site. Because the bulk of the seed bank at each site resembles its site vegetation more than that of another site, it is not possible to predict succession.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08618.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Water use patterns of two California chaparral shrub species, chamise(Adenostoma fasciculatumH. and A.) and Stanford manzanita(Arctostaphylos stanfordianaParry), were compared during summer drought. Observations of diurnal and seasonal courses of shoot water potential, leaf conductance and transpiration revealed that chamise was more conservative in water use than manzanita. Evidence obtained cast doubt on a hypothesis previously proposed to explain an anomalous pattern of shoot water potential in chamise.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08619.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Agastachesect.Agastacheconsists of seven species in North America and one disjunct in eastern Asia. Starch‐gel electrophoresis of enzymatic proteins was employed to assess genetic relationships among these species and to estimate the amount of genetic divergence between the North American and Asian populations. Species of the western United States appear to be better adapted for outcrossing than are the others and are much more genetically variable, with higher levels of heterozygosity per individual, more alleles per species, and higher percentages of polymorphic loci per population. Nonmetric multidimensional scaling of Nei's genetic distances among 32 populations partitioned the section into four discrete groups: 1)A. nepetoides(eastern North America), 2)A. scrophulariifoliaandA. foeniculum(eastern and central North America), 3) the four species of the western United States (A. urticifolia, A. occidentalis, A. parvifoliaandA. cusickii)and 4)A. rugosa(eastern Asia). AsianAgastache, separated from its American congeners for over twelve million years, differed from American populations at two of fifteen loci surveyed. Nei's genetic distances between Asian and North American populations ranged from 0.2877 to 0.6734.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08620.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Plasmolytic studies utilizing a graded series of mannitol solutions (0.1–1.4 M in 0.1 M increments) were conducted on adventitious roots ofZea maysto determine solute concentrations of cell types at various locations in the root. Results indicated that mature sieve‐tube members had the highest solute concentration as determined by their C50(the estimated mannitol concentration plasmolyzing an average of 50% of a given cell type) of any cell type in the root. In tissue 12 cm from the tip, C50values calculated for proto‐ and metaphloem sieve‐tube members were 1.15 and 1.19 M, respectively, while in tissue 0.5 cm from the root tip, values for the same cell types were 0.68 and 0.46 M, respectively. The C50values for sieve elements in tissue 5 cm from the tip were intermediate (1.08 and 1.11 M). Although the companion cells generally plasmolyzed at nearly the same concentrations of mannitol as the sieve elements, their C50values were slightly lower than adjacent mature sieve elements. The lowest C50(0.35 M) for any cell type examined was associated with meristematic cells in tissue 0.1 cm from the root tip. Taken collectively, the results indicate that positive concentration gradients exist between mature sieve tubes and meristematic cells of the root apex of maize.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08621.x

出版商:Wiley    

年代:1987

数据来源: WILEY