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Populations of the outbreeding perennial herb Silene dioica, growing on the islands of an archipelago in the Baltic Sea, are often diseased by the sterilising anther-smut fungus Microbotryum violaceum (synonym Ustilago violaceu). Since diseased host plants are sterilised, island populations with high disease incidences experience large reductions in the number of reproductive individuals. Here, we compared the genetic composition of diseased plants at six allozyme loci with that of the remaining reproductive individuals to determine whether this reduction changes the genetic composition of S. dioica island populations. We found a significant but small difference in genetic composition between diseased and healthy samples using analyses of multiple allelic types. We discuss our results in relation to changes in genetic differentiation among island populations and the impact of disease in the archipelago.

The effectiveness of single and repeated annual preharvest glyphosate applications (1 to 2 wk before crop harvest) to reduce Canada thistle populations was evaluated in field experiments near Bezanson, AB, Scott, SK, and St. Albert, AB. Single applications of glyphosate at 0.45 to 1.8 kg/ha at Bezanson and St. Albert reduced Canada thistle shoot density by more than 75% but in the three experiments at Scott 1.8 kg/ha was required to consistently obtain a similar reduction. Four consecutive, annual applications of glyphosate at 0.45 kg/ha or more did not eliminate Canada thistle but reduced shoot densities by more than 98% at Bezanson. At Scott, similar reductions occurred in two of three sites following two consecutive, annual preharvest applications of glyphosate at the same rates. In the third Scott site the 1.8 kg/ha rate of glyphosate provided a similar reduction but lower rates did not. At Bezanson, barley yields following the first, second, and third applications of glyphosate at 0.45 kg/ha or more were 14% greater than check plots where MCPA was applied in the spring. Yields of wheat seeded 1 yr after a single application of glyphosate at St. Albert were 26% greater than from unsprayed checks. Barley yields seeded 1 yr after each glyphosate application at Scott were not affected because Canada thistle populations were sparse.

The ability to use the relations between visible landmarks to locate nonvisible goals (allocentric spatial coding) underlies success on a variety of everyday spatial orientation problems. Little is known about the development of true relational coding in infancy. Ninety-six 6-, 8.5- and 12-month-old infants were observed in a peekaboo paradigm in which they had to turn to a target location after displacement to a novel position and direction of facing. In a landmark condition, the target position was located between two landmarks, contrasted with a control condition in which no distinctive landmarks were provided. Six-month-old infants performed poorly in both conditions, 8.5-month-olds were significantly better with the landmarks, and 12-month-olds solved the task with or without landmarks. A follow-up study confirmed that the 8.5-month-olds used both landmarks to solve the task. This demonstration of allocentric spatial coding in 8.5-month-old infants shows earlier competence than that found in previous work in which only infants at the end of the first year were able to use landmarks relationally.

The effects of grazing, fertilizing, and seeding on persistence of herbaceous species was monitored by point quadrat about every second year from 1975 to 1989 in a low-fertility pasture in the aspen parkland vegetation zone of east-central Saskatchewan, Canada. Ground cover response to continuous grazing was contrasted with that of 4- and 6-paddock rotationally-grazed areas fertilized in the fall of every other year with 90 kg N, 45 kg P2O5, 10 kg S ha-1. The original vegetation in 2 paddocks of the 6-paddock system was replaced with Russian wildrye (Psathyrostachys juncea (Fisch.) Nevski) in 1976, and in 1 of the other 4 paddocks in turn with smooth brome (Bromus inermis Leyss.)-alfalfa (Medicago sativa L.) in 1979 and 1981, crested wheatgrass (Agropyron cristatum (L.) Gaertn.) in 1983, and a meadow brome (Bromus riparius Rehm.)-alfalfa mix in 1985. Initially, smooth brome and creeping red fescue (Festuca rubra L.) dominated the vegetation with ground cover estimates of 10-20% and 40-60%, respectively. Alfalfa ground cover was less than 1%. With the changes in management, Kentucky bluegrass (Poa pratensis L.) replaced creeping red fescue. Alfalfa increased until 1980 and then declined to its original level, apparently in response to precipitation trends. Russian wildrye almost died out and was replaced by brome and Kentucky bluegrass. Reseeding with smooth bromegrass-alfalfa did not consistently increase brome ground cover beyond that obtained by rotational grazing and fertilization, and increased alfalfa only temporarily. Cultivation during the summer before spring seeding resulted in partial recovery of the old vegetation and invasion by Kentucky blue-grass. Total ground cover varied from year to year in response to spring precipitation. Forbs usually increased after reseeding, but declined to their original levels within 5 years.

Extending the present 4 month grazing season in the Aspen parklands of western Canada is of major economic interest to cow-calf producers. A long-term experiment was conducted on 375 ha to compare the present practice of continuous grazing with no fertilizer to a rotational grazing system of 4 paddocks fertilized in alternate years with 90 kg N, 45 kg P2O5, 10 kg S ha-1 and a 6 paddocks rotational grazing system including fertilizing and species replacement by cultivation and reseeding. Compared to the continuously-grazed control, the grazing period was extended by 14-days on the 4-paddock rotation system, and by a further 15-days on the 6-paddock rotation system, divided about equally between spring and fall. Forage yield, cow weight gains and calf growth were significantly improved, and year-to-year variation in forage yield and animal weight gain was reduced. In the 6-paddock rotation system, breaking 1 paddock at a time in summer after grazing, and reseeding the following spring caused no noticeable reduction in grazing capacity. Replacing the bromegrass (Bromus inermis Leyss.) dominated vegetation in 1 of the 6 paddocks with an early-growing grass contributed to the grazing season extension. Crested wheatgrass (Agropyron cristatum (L.) Gaertn.) performed well in this role; Russian wildrye (Psathyrostachys juncea (Fisch.) Nevski) died out within 6 years of seeding.

An investigation of the acoustic correlates of stress or accent in infant vocalizations was undertaken using five English‐ and five French‐learning participants at two developmental points, the onset of word use (10–13 months) and late in the single‐word period (14–19 months). A data base of 555 disyllabic utterances (words and babble) was digitized from naturalistic recordings and quantified acoustically by indices of duration, amplitude, and fundamental frequency (F0). Cluster analysis as well as the results of perceptual judgments (i.e., both a bottom‐up and a top‐down approach) revealed a developmental trend toward the adult prosodic system. In addition, acoustic comparisons of French and American infants at both developmental points revealed differences in their use of amplitude, F0, and duration to accent a syllable. The differences were traceable to the adult patterns for the respective adult languages. These results suggest that infants’ perceptual attunement to prosody in the prelinguistic period...

Distinct isozyme profiles initially discovered among a small collection of Festuca plants from Bathurst Island, Canadian Arctic Archipelago, were further investigated. Isozyme and mor- phological data revealed a new tetraploid species Festuca edlundiae that is often associated with F. hyperborea. The species differ in having distinct isozyme profiles for at least five isozymes, and in the size and shape of the flag leaves, the size of spikelets, and the shape of the upper glumes. Plants with the isozyme profile of F. edlundiae were collected from eight sites on five of the Queen Elizabeth Islands in 1992, and from Ellesmere Island in 1993. All sites are highly calcareous, with fine grained, mineral soils. A herbarium study found specimens from thirty other locations, including sites in northern Greenland and three from the former U.S.S.R. Morphological and isozyme characteristics used to distinguish F. edlundiae from F. baffinensis, F. brachyphylla, and F. hyperborea in the Canadian High Arctic are assessed, difficulties in identifying small plants and early season collections are documented, and a key to the four taxa, descriptions, and distribution maps are included.

1 If different genotypes have different relative fitnesses in different habitats, genetic diversity may be maintained in local populations by habitat selection. The spatial structuring of genetic variation within plant populations will thus be associated

Data were collected on epiphyte occurrence on tree trunks of four diameter classes in a Guatemalan cloud forest in order to document the vascular epiphyte flora and to explore aspects of species associations. Of the 68 species recorded, the largest groups were the Orchidaceae (29 species) and the Polypodiaceae (18 species). Conditional clustering and constellation analyses revealed associations of small, closely related species on smaller and consequently younger trunks, and associations of larger, less closely related species on larger, and hence older, trunks