Smith Var Research Articles

Notes on Some Scrophulariaceae from China

Notes on Some Scrophulariaceae from China

Ultrastructure of the extracellular matrix and taxonomy of Eudorina, Pleodorina and Yamagishiella gen. nov. (Volvocaceae, Chlorophyta)

Abstract Vegetative colonies of Pandorina unicocca Rayburn et Starr, four taxa of Eudorina [E. elegans Ehrenberg (type species), E. illinoisensis (Kofoid) Pascher, E. unicocca G.M. Smith var. unicocca andE. unicocca var. peripheralis Goldstein] and two species of Pleodorina [Po californicaShaw (type species) and P. indica (Iyengar) Nozaki] were examined with electron microscopy in order to characterize the structure of the extracellular matrix. Each cell of the colonies of all the taxa examined was tightly enclosed by a dense fibrillar zone of the extracellular matrix (cellular envelope) with sparse fibrillar material filling the space outside the cellular envelopes within the tripartite colonial boundary of the matrix. This arrangement is essentially different from that of Pandorina morum (O.F. Miiller) Bory (type species) and P. colemaniae Nozaki. As Eudorina and Pleodorina both have anisogamous sexual reproduction with sperm packets (bundles of male gametes), a new genus, Yamagishiella Nozaki, is propo...

Polymorphism in the desmidStaurastrum pentacerum(Wolle) G. M. Smith

Morphological studies, with emphasis on apical radiation, were carried out on phytoplankton samples from several Muskoka District (Ontario, Canada) lakes which contained desmids identifiable as Staurastrum pentacerum (Wolle) G. M. Smith var. pentacerum (5-radiate), S. pentacerum var. hexacerum Irenee-Marie (6-radiate), S. pentacerum var. tetracerum (Wolle) G. M. Smith (4-radiate) and Staurastrum sublongipes G. M. Smith (3-radiate). These taxa could not be distinguished on any morphological character except apical radiation. Cells which had differing patterns of radiation on the two semicells were observed in almost all populations. These dichotypical (“Janus”) forms indicate that apical radiation is a variable character. Thus these four taxa belong to a single highly polymorphic species, S. pentacerum.

Gas Exchange of Three Cool Semi-Desert Species in Relation to Temperature and Water Stress

Arid and semi-arid environments present severe constraints to plant life. Species in arid habitats have evolved different adaptive strategies for avoiding or enduring stress conditions and some involve the processes of gas exchange. Some perennial species may exhibit high photosynthetic and growth rates only during seasons when precipitation and temperature conditions are favourable, becoming largely dormant during harsher periods. Other species appear to be capable of enduring stress conditions through physiological and morphological changes and pose some of the most intriguing and challenging questions from the standpoint of adaptations involving gas exchange. The two shrub species investigated in the present study, Artemisia tridentata Nutt. subsp. tridentata and Gutierrezia sarothrae (Pursh) Britt. & Rusby, are both species possessing the C3 pathway of photosynthesis (Welkie & Caldwell 1970; Williams & Markley 1973). They remain photosynthetically active during periods of water and heat stress, and are frequently found flourishing side by side. These two species none the less exhibit striking differences in phenology and morphology. Artemisia tridentata may attain heights of up to 1-5 m, is deep-rooted, possesses rather dense foliage all the year and has predominantly woody stems. Gutierrezia sarothrae is a much smaller suffrutescent shrub (often c. 0f2 m tall), dies back to a low, woody central stem every year and possesses a shallow, fibrous root system, sparse foliage, and a relatively high proportion of green stem material. In the northern part of its range, this species remains green and vigorous throughout the growing season, even during seasonal drought periods. The general goal of this study was to define differences in the adaptive strategies of gas exchange which allow these species to survive in sirnilar habitats in the same community. A third species present in this community, the perennial bunchgrass Agropyron spicatum (Pursh) Scribn. & Smith var. inerme Heller, which becomes photosynthetically dormant during stress periods, was also studied to present gas exchange characteristics of a species which avoids active gas exchange under extreme physical conditions.t Seasonal changes in the morphological characteristics of each species have been correlated with gas exchange responses. Effects of irradiation were noted, but primary emphasis was placed on gas exchange responses to water stress and temperature.

Mosses Associated with Waterfalls in Central Labrador, Canada

One hundred and thirty moss species (including 20 new to Labrador) were collected within reach of spray from four subarctic waterfalls in central Labrador. The floristics, ecology, and phytogeography of these species are discussed, along with possible reasons for the enriched bryoflora of spray zones. Some northern and some southern mosses appear to be restricted to spray zones in central Labrador, but the majority of spray zone species belong to a wide-ranging north temperate-subarctic element. The spray zone environment tends to favour snow-bed mosses, the more calciphilic mosses, and hydrophilic mosses, and allows bryophytes to successfully outcompete lichens as the dominant cryptogams in these restricted sites. Polytrichastrum alpinum (Hedw.) G. L. Smith var. brevifolium (R. Br.) Brassard is a new combination. In 1970 and 1971 I spent several months investigating the bryophyte flora of central Labrador, centred around Churchill Falls (Fig. 1). The most intensive work was done in the vicinity of Churchill Falls (within the zone reached by spray from the falls) and in spray zones of three other waterfalls in the same general area (Fig. 2). This paper presents a list and assessment of the mosses associated with these subarctic waterfalls, and the importance of such microclimatic enclaves to the bryoflora of central Labrador as a whole. A separate paper now in preparation will treat the liverworts in similar fashion. Few parts of central Labrador have been investigated for bryophytes. Crum and Kallio (1966) reported the only substantial list of mosses and liverworts from this area. As was to be expected, my studies have added several species to the known bryoflora of Labrador and numerous species to the bryoflora of the Churchill Falls region. The present paper, however, deals only with mosses directly associated with spray zones of waterfalls; in general these have a bryoflora much more diverse than that of the surrounding spruce-Cladonia woodland and subarctic taiga. It is these small humid oceanic oases within the continental subarctic taiga which have provided most of the additions to the bryoflora of the region. 1 Studies in Biology from Memorial University No. 347. I thank the International Biological Programme, the National Research Council of Canada (Grant A-6683), and Memorial University for financial support. The Churchill Falls (Labrador) Corporation provided logistic support which greatly facilitated the field studies. I also thank Dr. Howard Crum, Dr. Timo Koponen, Dr. Dale Vitt, and Mr. Harry Williams for identifying difficult specimens. Dr. Victor Snieckus and Mr. Ed Delaney provided assistance with some aspects of the field work. 2 Department of Biology, Memorial University, St. John's, Newfoundland, Canada. This content downloaded from 157.55.39.157 on Fri, 08 Jul 2016 04:31:57 UTC All use subject to http://about.jstor.org/terms 1972] BRASSARD: MOSSES OF LABRADOR WATERFALLS 517

Some new species and distribution records of Rhizopogon in North America

The following 12 new species and two varieties of Rhizopogon are described from collections made around Nelson, British Columbia, and Santa Fe, New Mexico: R.amoenus Harrison and Smith, R.armeniacus Harrison and Smith, R. canadensis Harrison and Smith, R. cinnamomeus Harrison and Smith, R. columbianus Harrison and Smith, R. inversus Harrison and Smith, R. pachydermus Harrison and Smith, R. pinyonensis Harrison and Smith var. pinyonensis, R. pinyonensis var. sublutescens Harrison and Smith, R. pinyonensis var. albidus Harrison and Smith, R. praestans Harrison and Smith, R. singularis Harrison and Smith, R. tephrogleba Harrison and Smith, and R. vestitus Harrison and Smith. Additional information is presented on four recently described species, and the ranges of 29 species are extended. It has been found that, when rainfall conditions are favorable, a distinctive and characteristic Rhizopogon flora occurs under pinyon pines in the pinyon pine – juniper forests of the arid regions of the south west.

The occurrence of a male of the prosobranchPotamopyrgus jenkinsi(Smith) var.carinataMarshall in the Thames at Sonning, Berkshire

The occurrence of a male of the prosobranch<i>Potamopyrgus jenkinsi</i>(Smith) var.<i>carinata</i>Marshall in the Thames at Sonning, Berkshire