The Effects of Root Pruning on the Water Relations of Helianthus annuus L.

Four-week-old Helianthus annuus plants, grown in both soil andliquid culture, were root pruned at the point of root attachmentto the stem. Transpiration, leaf water potential and leaf conductivitywere monitored for several days after pruning. Pruning loweredtranspiration and leaf conductivity in amounts proportionalto the amount of pruning. In some experiments pruning causeda slight lowering of leaf water potential, while in others nopruning effect could be found. The effects of pruning varieddepending upon culture conditions, with greater effects beingfound in soil and unaerated liquid culture than in aerated liquidculture. Soil water potential did not appear to have a stronginfluence on the magnitude of the pruning effect. The effectsof root pruning are less than would be predicted by an Ohm'sLaw analysis of flow; possible reasons for this are discussed.     

Fine Structure of an Unidentified Protozoon in the Epithelium of Rainbow Trout Exposed to Water with Myxosoma cerebralis*

SYNOPSIS. An intracellular protozoon was discovered in the epithelium of young rainbow trout (Salmo gairdneri) exposed for as short a time as 1 hr to water known to contain infective stages of Myxosoma cerebralis. Light- and electron-microscopic examination of this tissue revealed what appeared to be a proliferative stage (presumptive schizont) of a sporozoon; other possible stages in the life cycle were also observed. The relationship of this unidentified protozoon to M. cerebralis remains unresolved.     

HORIZONTAL ANGULAR DISCRIMINATION BY AN ECHOLOCATING BOTTLENOSE DOLPHIN TURSIOPS TRUNCATUS

ABSTRACT

A bottlenose dolphin was tested on its ability to echoically discriminate horizontal angular differences between two arrays of vertical, air-filled, PVC rods. The blindfolded dolphin was required to station in a submerged, vertically-oriented hoop, 2 radial metres from the stimuli, and indicate whether an array with four rods (S+) was to the left or the right of an array with two rods (S-), by pressing a corresponding paddle. The angular separation between the rods within each array (θ_w) was maintained at 2 degrees but the angular separation between the two arrays (θ_b) was varied to produce angular differences (δθ = θ_b-θ_w)ranging from 0.25 degrees to 4 degrees. A modified method of constant stimuli was used to test for angular discrimination ability, and yielded a psychometric function having a 75% correct threshold of 1.6 degrees. This threshold fell between the passive listening minimum audible angle thresholds of 0.9 degrees for click signals and 2.1 degrees for a pure tone signal (Renaud & Popper 1975). Analyses of response times, number of clicks and inter-click intervals failed to detect any significant adaptive behaviour occurring as the task became more difficult. These results help to define angular resolution capabilities of dolphin sonar that may play an important role in representing spatial information in the dolphin's environment.     

How cold‐adapted flightless flies dispersed over the northern hemisphere: phylogeny and biogeography of the snow fly genus Chionea Dalman (Diptera: Limoniidae)

A phylogeny of the 37 known species and subspecies of the micropterous snow fly genus Chionea Dalman is presented using adult morphological characters. The genus contains two major clades: a strictly Palaearctic clade, and a combined Nearctic‐Palaearctic clade with representatives in the Nearctic and Western Palaearctic regions. As there is little congruence between the recovered phylogeny of Chionea and the currently used subgeneric division in Chionea s.s. and Sphaeconophilus Becker, we propose to abandon the use of subgeneric taxa in Chionea. A strictly morphological analysis appears to be insufficient to fully resolve the phylogeny of the genus at the species level, and future molecular work should provide additional evidence for the establishment of relationships among the members of Chionea. The large‐scale historical biogeography of Chionea was analysed using dispersal‐vicariance analysis. The initial distribution area of the genus probably extended in the Eastern Palaearctic, and the Nearctic and the origin of Chionea could be dated in the Late Cretaceous. The various dispersal and vicariance events that led to the major speciation events in the genus are set against major paleogeographic developments. The ancestor of the Western Palaearctic group in the second major clade originated from the Nearctic. The presence of the cold‐adapted Chionea in currently temperate to warm climatic zones in the southern parts of its distribution was analysed using ecological niche modelling. It appears that prolonged periods of climate cooling, as occurred during the Last Glacial Maximum, enabled Chionea to cover large parts of central and southern Europe and reach the southern distribution areas where the genus is present today. A similar biogeographic pattern was less evident in the Nearctic region.     

LOWER DEVONIAN GRAPTOLITES FROM SOUTHEASTERN ALASKA

The youngest zones of Monograptus occur in Devonian black shale and slate along the western shore of Prince of Wales Island and on Noyes Island, southeastern Alaska. The following five species of Monograptus, in close association with vascular plants and marine shelly faunas, indicate a Praguian, (Siegenian to Early Emsian), late Lower Devonian and possibly early Middle Devonian age: M. yukonensis Jackson & Lenz, M. n. sp. aff. yukonensis ? Jaeger & Stein, M. aeqimbilis notoaequakilis Jaeger & Stein, M. pacificus Jaeger n. sp. and M. craigensis Jaeger n. sp. The yukonensis zone containing M. craigensis in its upper part is followed stratigraphically higher by the M. pacificus zone – the youngest occurrence of Monograptus. The new species belong to the M. uncinatus group and, like most Praguian monograptids, have long dorsal tongues on their siculae. M. craigensis and M. pacificus increase to seven the number of species of Monograptus known from the Praguian. On the basis of the Alaskan material, the geographical distribution of M. aequabilis notoaequabilis now includes North America in addition to previously recorded occurrences in Australia, Southeast Asia, and Europe. This broad geographic distribution suggests that the last survivors of Monograptus had worldwide distribution and a rather uniform assemblage of species.