MORPHOLOGY AND ANATOMY OF NEW SPECIES OF SCHIZAEA AND ACTINOSTACHYS

The gametophyte, old embryo, and sporophyte of Schizaea pseudodichotoma sp. nov., sporophyte and female parental gametophyte of S. diversispora hybr. nov. (S. pseudodicholoma X probably S. dichotoma), sporophyte of S. rhacoindusiata sp. nov., and gametophyte, old embryo, and sporophyte of Actinostachys macrofunda sp. nov. are described. The taxonomy of Schizaea is discussed and the system of Diels is strongly supported. The two sectional names used by Diels, Euschizaea Hook, and Lophidium Rich, are replaced by Pectinatae Prantl and Schizaea respectively. The prime morphological significance of Schizaea pseudodicholoma lies in its leafless embryo and its simple leaf differing from other species in its section, and that of Actinostachys macrofunda lies in its reduction to nearly complete heterotrophic existence and its frequent multiple annulus. Fungal hyphae have been traced from Schizaea and Actinostachys through the substratum and into root nodules of Casuarina and into roots of two other angiosperms.     

ELECTRON MICROSCOPY OF WOOD OF CALLIXYLON AND CORDAITES

Replicas and ultrathin sections of the wood of two Paleozoic genera, Callixylon and Cordaites, were examined with the electron microscope. The pattern of wall layering of Callixylon closely resembles that of extant plants. An electron-dense compound middle lamella markedly thickened at the corners of cells, a thin, electron-transparent S₁ layer of the secondary wall, and a thick, electron-dense, partially decayed S₂ layer of the secondary wall are evident in transverse sections of tracheids. No S₃ layer seems to be present. The structure of the bordered pit-pairs of Callixylon is described in detail. The slitlike outer pit apertures are conspicuously narrower and shorter than the inner pit apertures. Both sections and replicas of the bordered pit-pairs display pit membranes lacking tori. Microfibrillar structure is obscure in both sections and replicas of Callixylon wood. Replicas of the bordered pits of Cordaites wood are very similar to those of Callixylon. Pit membranes lack tori, and microfibrillar structure is not very discernible. Knowledge about the evolution of the torus is summarized. It is postulated that the type of pit membrane of Callixylon and Cordaites, which is very homogeneous in structure and lacks a torus, represents a primitive condition among gymnosperms from which structurally more complex pit membranes and the torus later evolved.     

EMBRYOLOGY AND KARYOMORPHOLOGY OF LACTORIDACEAE

The embryology and karyomorphology of Lactoris fernandeziana, representing the monotypic family Lactoridaceae, were studied in an attempt to clarify its relationships. Embryologically, Lactoris is characterized by a combination of many generalized, plesiomorphic features, which are mostly shared with Magnoliales and partly shared with Laurales and Piperales, and some specialized, apomorphic features including a tenuinucellate ovule, a small nucellus with early disintegrating nucellar tissue, a nonmultiplicative outer integument, an endothelium, and haustorial endosperm. Karyomorphologically Lactoris is confirmed to have 2n = 40 at metaphase, probably as a tetraploid of x = 10, and more or less distinctive features at inter- and prophase. Comparisons based on its embryological and karyomorphological features suggest that Lactoris is not closely related to any other family. Based on evidence from various sources, we hypothesize that an evolutionary line was derived from a common ancestor with Magnoliales, and then diverged into Lactoris, which retains many primitive magnolialean features, and Piperales (and possibly other groups) with more specialized characteristics. Lactoris seems best placed in its own order, Lactoridales, near Piperales.     

ANATOMY AND AFFINITIES OF PENTHORUM

The genus Penthorum L. consists of two species of perennial herbs, P. sedoides of eastern North America and P. chinense of eastern Asia. Penthorum has long been considered intermediate between Crassulaceae and Saxifragaceae. An anatomical study of both species was undertaken to contribute to a better understanding of the relationships of these plants. Prominent anatomical features of Penthorum include: an aerenchymatous cortex and closely-spaced collateral vascular bundles of stems; one-trace unilacunar nodes; brochidodromous venation, rosoid teeth bearing hydathodes, and anomocytic stomata of leaves; angular vessel elements with many-barred scalariform perforation plates and alternate to scattered intervascular pits; thin-walled non-septate fiber-tracheids; abundant homocellular erect uniseriate and biseriate rays; and absence of axial xylem parenchyma. In general, Penthorum possesses neither the morphological nor the anatomical synapomorphies which define Crassulaceae, and features shared with Saxifragaceae are largely symplesiomorphous. Thus Penthorum is probably best classified in the monogeneric Penthoraceae.     

COMPARATIVE CYTOLOGY OF ULOTHRIX AND STIGEOCLONIUM1

This investigation describes the cytology of the ulotrichalean genera Ulothrix and Stigeoclonium. Cellular organization is similar to the degree that interphase cells of the 2 genera cannot be distinguished with certainly. In Stigeoclonium, the nuclear envelope becomes disrupted at the end of prophase, and centrioles enter the nucleoplasm. At metaphase the nuclear envelope is again intact, and some of the spindle tubules appear to be contiguous with the nuclear envelope. The spindle in Ulothrix is essentially open with, no attachment of spindle tubules to the nuclear envelope and with, centrioles on the spindle-cytoplasm interface at the spindle poles. Spindle poles are blunt in Stigeoclonium and pointed in Ulothrix. Cytokinesis is by cell plate formation in both genera, but there is no phragmoplast.     

SPECIES OF OCEANIC DINOFLAGELLATES IN THE GENERA DISSODINIUM AND PYROCYSTIS: INTERCLONAL AND INTERSPECIFIC COMPARISONS OF THE COLOR AND PHOTON YIELD OF BIOLUMINESCENCE1

We have examined aspects of the bioluminescence of 5 clones of Dissodinium, 1 clone of Pyrocystis acuta, 4 clones of Pyrocystis fusiformis, and 5 clones of Pyrocystis noctiluca. All clones produced the same color bioluminescence with an intensity peak near 474 nm. The in vivo emission spectra of these clones agreed with those previously determined, for 4 other species of marine dinoflagellates. The amount of light emitted by the dinoflagellates in scotophase when mechanically stimulated to exhaustion was determined for most of the clones. The largest species, P. noctiluca and P. fusiformis, emitted 37–89 × 10⁹ photons cell^?1 and 23–62 × 10⁹ photons cell^?1, respectively, about a thousand, times as much light as Gonyaulax species. Pyrocystis acuta emitted 3–6 × 10⁹ photons cell^?1. Three of the 5 clones of Dissodinium were bioluminescent. The range for 3 clones was 5–13 × 10⁹ photons cell^?1. All 5 clones of Dissodinium are morphologically distinct. Both the clones of Dissodinium and Pyrocystis produced much higher numbers of photons per cell nitrogen (ca. 7–50 times) than Gonyaulax polyedra or Pyrodinium bahamense. The data suggested that enzyme turnover occurred in the reactions producing light during mechanical stimulation of Dissodinium and Pyrocystis species.     

MEASUREMENTS AND MOULT OF FIVE SPECIES OF BULBUL FROM MOÇAMBIQUE AND MALAŴI

Summary

Hanmer, D. B., 1978. Measurements and moult of five species of bulbul from Moçambique and Mala?i. Ostrich 49:116-131.

The wing length, weight and moult of five species of bulbul, Blackeyed Pycnonotus barbatus, Sombre Andropadus importunus, Yellowbellied A. flaviventris, Terrestrial Phyllas-trephus terrestris and Yellowspotted Nicator Nicator gularis, are given for two localities in tropical lowland (Mopcia, Moçambique and Nchalo, Mala?i). The characters identifying immatures and the length of time these are retained, are given with reference to skull pneumatization, retrapped birds and the breeding season, for Pycnonotus barbatus, Andropadus intportunus and Phyllastrephus terrestris. Weights are compared with some published for other parts of Africa. The months during which moult occurred are given. Duration and timing of primary moult and its relation to the breeding season, are given for Pycnonotus barbatus, Andropadus importunus and Phyllastrephus terrestris. The age at which immatures moult is given for these three species. Instances of interrupted moult are mentioned.     

ELECTRON MICROSCOPY OF CARTERIA AND CHLAMYDOMONAS

Cultures of Chlamydomonas eugametos, Chl. sp., Carteria eugametos, C. crucifera, C. radiosa, and C. sp. were examined with the electron microscope to determine generic differences between Carteria and Chlamydomonas at the ultrastructural level. The ultrastructure of the flagella, mitochondria, dictyosomes, nuclei and ground substance was noted to be similar in all species. The cellular boundary of all species except Chlamydomonas eugametos contains a 250 A intermediate layer of unknown chemical composition between the fibrillar cellulose wall and the outer capsule layer. Four structural features other than the number of flagella distinguish Carteria from Chlamydomonas: the intermediate layer of the cellular boundary, the chloroplast, the pyrenoid and the eyespot. Only in the Carteria species is the intermediate layer traversed by striations or 12-mμ-wide bars. Striations in the cellulose wall surrounding the flagellar channels also appear in Carteria eugametos and C. crucifera. The chloroplast lamellae of the Carteria species are grouped into discrete stacks of invaginated thylakoids termed pseudograna. The chloroplast lamellae of Chlamydomonas are broad and sheet-like and are also invaginated although less frequently than are the pseudograna of Carteria. The phenomenon of infolding of the chloroplast lamellae is suggested as a general developmental process in the formation of new thylakoids. In Carteria, single thylakoids traverse the pyrenoid and there are 2 rows of granules in the eyespot. Favorable micrographs of the eyespot indicate that the granules may be osmiophilic granules of the chloroplast chemically modified for a photoreceptive function.     

MORPHOLOGY AND TAXONOMY OF PROROCENTRUM MEXICANUM AND REINSTATEMENT OF PROROCENTRUM RHATHYMUM (DINOPHYCEAE)1

Dinoflagellates collected during red tide events in Bahia Mazatlan, Mexico during the early spring of 1999 and 2000 appeared under LM to belong to Prorocentrum mexicanum Osorio‐Tafall. Observations with SEM of those populations showed marked differences in shape and microornamentation from the related species, Prorocentrum rhathymum Loeblich III, Sherley and Schmidt. In P. mexicanum, the presence and dimensions of poroids, the uneven distribution of trichocyst pores not located in depressions, and the general architecture of the periflagellar region are more closely related to Prorocentrum caribbaeum Faust. Also, P. mexicanum has a three‐horned (sometimes two‐horned) spine and is deeper in the anterior than the posterior region, whereas P. rhathymum has a simple small spine and its sagittal view is oval. Furthermore, the number and distribution of trichocyst pores in the periflagellar area is different between the two species, being located on both valves in P. mexicanum and only on the right valve in P. rhathymum. To date, true P. mexicanum has been described only from plankton sampling, whereas P. rhathymum was frequently mentioned associated with floating detritus (macroalgae) but also forming red tides. Altogether, the evidence presented demonstrates that P. mexicanum (planktonic) and P. rhathymum (epibenthic) are distinct species and are not synonyms, as is often accepted.     

SHAPE AND FUNCTION OF THE SHELL: A COMPARISON OF SOME LIVING AND FOSSIL BIVALVE MOLLUSCS

• 1 The review is mainly concerned with Carboniferous non-marine Anthracosiidae and Myalinidae, of which only the shells are known, and with certain unspecialized non-byssate suspension-feeding bivalves which had smooth shells and burrowed shallowly.
• 2 Limited experimental evidence and observation of living bivalves suggest that in certain Recent siphonate species and in some members of the non-siphonate Anthracosiidae the shape of the shell was functionally related to movement through the sediment in the same way. Predicted optimum shapes of shells for downward burrowing and for upward near-vertical movement in sands and silts were apparently realized in the Anthracosiidae, which constituted a series of highly variable opportunistic assemblages. It is stressed, however, that the shape of the shell always appears to be a compromise between several functional requirements.
• 3 In both the early Anthracosiidae and in several analogous Recent marine genera, orientation of the long axis of the shell was the same for downward burrowing and for upward pushing, that is near the vertical, with posterior end upward.
• 4 Invasion of the Pennine late-Namurian delta took place when marine bivalves pushed upward, thereby avoiding sedimentation from delta lobes moving seaward relatively swiftly. The evolution of Carbonicola occurred at about this time (the Marsdenian Age) when the bivalves acquired a smooth elongate shell of ‘streamlined’ form, having a hinge plate with swellings and depressions on it (later to evolve into teeth). All these features tend to characterize the active shallow burrowers of today.
• 5 Entry into soft-bottom eutrophic conditions of fresh water is characterized in several unionids by increase in height/length (H/L or w/m) ratio of shell, in anterior end/length (A/L) and in obesity (T/L) (see Fig. 2, centre). These changes also took place in established faunas of Carbonicola characteristic of richly carbonaceous shales, in faunas of supposed Anthraconaia in more carbonaceous sediments of mid-and late-Carboniferous times in the U.S.A. and in Anthraconauta of the British late Carboniferous (Westphalian C and D). The genus Anthracosphaerium epitomizes the culmination of these trends in the Anthracosiidae, and species of the genus were probably epifaunal or shallowly infaunal active burrowers on soft bottoms in Westphalian upper A and B time.
• 6 Two contrasting patterns of growth characterize the shells of the widely variable unionid Margaritifera margaritifera. In the first, dorsal arching of the shell, with straightening and reflexion of the ventral margin, provides increased weight but decreased ligamental strength. In the second, in which the ‘hinge line’ tends to remain straight while the dorsal margin becomes more rounded and obesity increases, there is increased metabolic efficiency for active surface movement. The maintenance of these trends within the species, which may be regarded as secondarily opportunistic, affords a means of insurance for survival within the highly variable environments of fresh water. The same trends are recognizable in established faunas of Carbonicola, where it is likely that they performed the same function, as well as in Mesozoic and Cenozoic Unionidae.
• 7 The functional explanation outlined in paragraph (6) may be extended to provide an ecological meaning for Ortmann's ‘Law of Stream Distribution’, which states that obesity of unionid shells increases downstream. This applies broadly, within a fairly wide range of variation, a fact which again suggests ‘insurance’ of faunas against the variable hazards of fresh-water habitats.
• 8 In bivalves having considerable thickness of shell in relation to their size, and having strong umbonal development, specific gravity of the living bivalve is correlated with H/L and T/L ratios of the shell, as in the venerid Venerupis rhomboides. In this species, differences in the specific gravities of the bivalves, as well as their shape, appear to be functionally related to shallowly infaunal burrowing in different substrates.
• 9 The conclusions of paragraphs 6 and 8 provide a functional explanation, in terms of selection, for the palaeoecological ‘law’ of Eagar (1973), which is applicable to established faunas of Carbonicola in mid-Carboniferous time, and relates variational trends in two main groups of shells primarily to increases in the relative water velocities of the palaeoenvironments.
• 10 Where the growth of relatively unspecialized bivalve shells has been measured, allometric relationships have usually been found in H-L and T-L scatters. Logarithmic lines have two inflexions and linear scatters a sigmoidal form. A similar pattern of allometric growth has been found in both Carbonicola (H-L) and Anthraconauta (m-w). These patterns appear to be related to the optimum requirements of water-borne larvae, the initial byssal phase of settlement, when ability to burrow quickly is essential, and the main period of growth and activity. It is herein suggested that the final second inflexion, which indicates a falling off of gain in H/L and T/L ratios, may be a genetically controlled modification of the growth pattern which counteracts the operation of the ‘cube-square rule’ (of Thompson, 1942) and prolongs productive life.
• 11 Patterns of relative growth of the shell may be significantly modified by conditions of the habitat; both T/L and H/L ratios may be increased, with general reduction in size, in the less ‘favourable’ habitats. Both these ratios have been similarly modified, the one in the ‘natural laboratory’ of a lake formed by the damming up of streams, and the other in transplant experiments with living Venerupis. In both these latter cases, phenotypic changes took place in the same direction as those expected on the basis of natural selection. Direct response to environmental factors cannot therefore be ruled out as an agent in similar changes noted in Carbonicola and supposed Anthraconaia in paragraphs (5) and (9) and may have been operative in those of paragraphs (7) and (8).

     

POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF CIRCAEASTER,OF KINGDONIA,AND OF SARGENTODOXA TO THE RANUNCULALES

The pollen of three monotypic genera, Circaeaster, Kingdonia, and Sargentodoxa has been examined by light and scanning electron microscopy and in the case of the last genus, also by transmission electron microscopy. The type of tectum found in Circaeaster and Kingdonia, derivations of a compound layer of striae, has a restricted distribution in the Order Ranunculales. Of 64 genera examined in this order only six had species with a similar tectum. They include Achlys, Epimedium, Jeffersonia, and Vancouveria of the Berberidaceae s.l., the controversial Hydrastis, and Trollius of the Ranunculaceae. Circaeaster and Kingdonia have been considered as related since both have rare and primitive vegetative characteristics, the most notable being open dichotomous leaf venation. They are probably best treated as a ditypic family, Circaeasteraceae. The pollen of Sargentodoxa, especially the structure of the exine, closely resembles that of the Lardizabalaceae. However, the fruits of Sargentodoxa have been considered to be distinct from those of the Lardizabalaceae, suggesting that it be treated as a separate, but closely allied, family.     

KINETICS OF GLUCOSE TRANSPORT AND GROWTH OF CYCLOTELLA CRYPTICA REIMANN,LEWIN AND GUILLARD1,2

Growth rate as well as rate of glucose uptake of C. cryptica depends on glucose concentration in the medium according to saturation kinetics. The K _g for growth is 1.9 × 10^?5 M, and the K _t, for glucose transport is 5.8 × 10^?5 M. The maximum growth rate in the dark on glucose is considerably slower than the light-saturated growth rate at the same temperature, and does not appear to be determined by the capacity of the cell for glucose uptake. The glucose transport process is highly specific, and depends on energy metabolism. The Q ¹⁰ for the process is 2.2 (15–2.5 C). Glucose taken up by the cells is almost, quantitatively phosphorylated within 10 min, either through the transport process itself or by a high affinity kinase system in the cells.     

SYSTEMATIC ANATOMY OF THE FLOWER AND FRUIT OF COROKIA

Corokia, a genus of shrubs of New Zealand, eastern Australia, and certain Pacific islands, was first placed in Rhamnaceae, later in Cornaceae, and most recently next to Argophyllum, subfamily Escallonioideae, in Engler's monograph of the Saxifragaceae. Most manuals still list Corokia under Cornaceae from which it is readily excluded by several characters, including pluricellular T-shaped trichomes, ligulate petals, vascular bundles running longitudinally through the center of the inferior gynoecium, histology and germination of the woody endocarp, and a conspicuous subepidermal layer of tannin-containing cells. Corokia collenettei, endemic to the isolated island Rapa, retains the most primitive floral characters of the genus. Anatomical comparison of Corokia flowers with flowers of Argophyllum shows similarities that probably indicate affinity, but the relation of these two genera to others in Engler's subfamily Escallonioideae is unclear. Engler's inclusion of Berenice and Carpodetus with Corokia and Argophyllum in a tribe Argophylleae seems especially artificial.     

SOME OBSERVATIONS ON COLONIES AND ULTRASTRUCTURE OF THE FRUSTULE OF COENOBIODISCUS MURIFORMIS AND ITS TRANSFER TO PLANKTONIELLA1

The marine planktonic diatom Coenobiodiscus muriformis has been reinvestigated using light microscopy and scanning and transmission electron microscopy; as a result it is proposed, to transfer the species to the genus Planktoniella. The structure and formation of colonies are discussed and compared with data from an earlier study. Further details of valve and girdle baud structure have been ascertained and the exact form of the central and peripheral tubes has been described. The relationship of the present taxon to Thalassiosira and Coscinodiscus is discussed.     

CYTOGENETICS OF AGROPYRON FERGANENSE AND ITS HYBRIDS WITH SIX SPECIES OF AGROPYRON,ELYMUS, AND SITANION

Meiosis and mode of reproduction are described in Agropyron ferganense Drob., a perennial forage grass from Central Asia. This species is diploid (2n = 14); it exhibits normal meiosis and reproduces by cross-pollination. Hybrids were produced between A. ferganense and six species with known genome formulas: 1) North American A. spicatum (Pursh) Scribn. & Smith, an SS diploid (2n = 14), 2) Middle Eastern A. libanoticum Hack., an SS diploid (2n = 14), 3) North American A. dasystachyum (Hook.) Scribn., an SSHH tetraploid (2n = 28), 4) Eurasian A. caninum (L.) Beauv., an SSHH tetraploid (2n = 28), 5) North American Sitation hystrix (Nutt.) J. G. Smith, an SSHH tetraploid (2n = 28), and 6) South American Elymus patagonicus Speg., an SSHHHH hexaploid (2n = 42). Almost complete chromosome pairing in the A. ferganense x A. spicatum and A. libanoticum hybrids demonstrated that A. fergenanse is an SS diploid, but it is genetically isolated from the other SS diploids because of high sterility in the F₁ hybrids. S-genome diploids form a network of species that extend from the Middle East through Central Asia to western North America. Frequent occurrence of seven univalents and seven bivalents at metaphase I in the triploid hybrids of A. ferganense x A. dasystachyum, A. caninum and S. hystrix was consistent with the proposed genome formulas of SS for A. ferganense, SSHH for the three tetraploid species, and SSH for the hybrids. Chromosome pairing was highly variable in the A. ferganense x E. patagonicus hybrids; however, some cells had almost complete bivalent pairing, an expected observation in an SSHH hybrid from a cross between an SS diploid (A. ferganense) and an SSHHHH hexaploid (E. patagonicus). Various options were considered concerning the appropriate generic classification of the S-genome diploids, which are now commonly placed in Agropyron. The inclusion of these species in the genus Eiytrigia, as advocated by some Soviet taxonomists, appears to be a reasonable decision.     

HYBRIDIZATION AND CYTOTAXONOMY OF DICENTRA

Biosystematic relationships among species assigned to three subgenera of the genus Dicentra were investigated with respect to hybridization and chromosomal constitution and fertility of the hybrids. Four species of subgenus Dicentra, D. formosa, D. eximia, D. nevadensis, and D. peregrina, were intercrossed in various ways to form diploid, triploid, and tetraploid hybrids. Hybrids at the tetraploid level in this subgenus invariably were highly fertile. Triploid hybrids, as expected, were mostly very sterile. Diploid hybrids varied in this respect, but none was highly fertile. Crosses with two of the remaining four species of subgenus Dicentra produced no hybrids, but abundant seed was obtained in one instance. The two species of the subgenus Chrysocapnos, D. chrysaniha and D. ochroleuca, cross to produce a partially fertile tetraploid hybrid, but cross-pollinations involving these species with those of other subgenera failed. The single species of subgenus Hedycapnos, D. spectablis (diploid) produced no hybrids when cross-pollinated with members of the other two sections. These results are fully concordant with presumed affinities based on morphological similarity In addition, preliminary results of hybridization between the monocotyledonous D. peregrina and a number of dicotyledonous species of Dicentra are reported.     

THE GENOME CONSTITUTION AND PHYLOGENY OF ELYMUS AMBIGUUS

Two Elymus ambiguus Vasey & Scribn. collections from Utah and Idaho were 2n = 28, and the species behaved meiotically as an allotetraploid. The E. ambiguus plants were highly self-sterile, and they hybridized readily with Asian E. junceus Fisch. (2n = 14), E. karataviensis Roshev. (2n = 28), E. multicaulis Kar. & Kir. (2n = 28), and North American E. innovatus Beal (2n = 28). Chromosome pairing at metaphase-I in the E. ambiguus X E. junceus triploid hybrids indicated that one E. ambiguus genome was closely homologous with the E. junceus genome. Chromosome pairing in the tetraploid hybrids indicated that both E. ambiguus genomes were more or less homologous with the genomes of E. karataviensis, E. multicaulis, and E. innovatus. The basic genome formula of E. ambiguus may be written as JJXX, where J is the E. junceus genome and X is a genome of unknown origin. Chromosome pairing in the hybrids indicated that E. ambiguus is more closely related to North American E. innovatus than to the Asian species. The E. ambiguus X E. innovatus hybrids were the only hybrids that set seed. Gene flow between E. ambiguus and E. innovatus is biologically possible, but geographic separation of the species precludes natural introgression.     

WOLBACHIA AND THE EVOLUTION OF REPRODUCTIVE ISOLATION BETWEEN DROSOPHILA RECENS AND DROSOPHILA SUBQUINARIA

Endosymbiotic bacteria of the genus Wolbachia are widespread among insects and in many cases cause cytoplasmic incompatibility in crosses between infected males and uninfected females. Such findings have been used to argue that Wolbachia have played an important role in insect speciation. Theoretical models, however, indicate that Wolbachia alone are unlikely to lead to stable reproductive isolation between two formerly conspecific populations. Here we analyze the components of reproductive isolation between Drosophila recens, which is infected with Wolbachia, and its uninfected sister species Drosophila subquinaria. Laboratory pairings demonstrated that gene flow via matings between D. recens females and D. subquinaria males is hindered by behavioral isolation. Matings readily occurred in the reciprocal cross (D. quinaria females × D. recens males), but very few viable progeny were produced. The production of viable hybrids via this route was restored by antibiotic curing of D. recens of their Wolbachia symbionts, indicating that hybrid offspring production is greatly reduced by cytoplasmic incompatibility in the crosses involving infected D. recens males. Thus, behavioral isolation and Wolbachia-induced cytoplasmic incompatibility act as complementary asymmetrical isolating mechanisms between these two species. In accordance with Haldane's rule, hybrid females were fertile, whereas hybrid males invariably were sterile. Levels of mtDNA variation in D. recens are much lower than in either D. subquinaria or D. falleni, neither of which is infected with Wolbachia. The low haplotype diversity in D. recens is likely due to an mtDNA sweep associated with the spread of Wolbachia. Nevertheless, the existence of several mtDNA haplotypes in this species indicates that Wolbachia have been present as a potential isolating mechanism for a substantial period of evolutionary time. Finally, we argue that although Wolbachia by themselves are unlikely to bring about speciation, they can increase the rate of speciation in insects.     

THE EFFECT OF TEMPERATURE AND PHOTOPERIOD ON THE DEVELOPMENT OF GEOGRAPHICALLY ISOLATED POPULATIONS OF FUNARIA HYGROMETRICA AND WEISSIA CONTROVERSA

Geographically isolated populations of Funaria hygrometrica Hedw. and Weissia controversa Hedw. were cultured under controlled axenic conditions in the laboratory to determine the developmental variability found between and within two species of widespread distribution. Funaria plants were found to grow more rapidly than those of Weissia; the latter could not be induced to complete the life cycle in culture, and generally had a less broad tolerance to environmental extremes than did Funaria. Optimum temperatures of 30 C for spore germination and 25 C for protonematal growth and gametophore formation were observed in all populations of Funaria. Gametangial formation required cooler temperatures in all populations; however, optimal temperature requirements and sporophytic growth characteristics were population-dependent. The temperature responses of the various stages of the life cycle correlate well with seasonal temperature fluctuations that might be expected in nature. The presence of ecological races in Funaria hygrometrica is demonstrated in the behavior of the reproductive stages of the life cycle.     

POLYSACCHARIDES FROM THE ENVELOPES OF HETEROCYSTS AND SPORES OF THE BLUE-GREEN ALGAE ANABAENA VARIABILIS AND CYLINDROSPERMUM LICHENIFORME1

The polysaccharides from the envelopes of heterocysts of Cylindrospermum licheniforme Kütz., and of heterocysts and spores of Anabaena variabilis Kütz., like those from the differentiated cells of Anabaena cylindrica Lemm., have a 1,3-linked backbone consisting of glucosyl and mannosyl residues in a molar ratio of approximately 3:1. As is the case with A. cylindrica the polysaccharides from A. variabilis and from the heterocysts of C. licheniforme have terminal xylosyl and galactosyl residues as side branches. In addition, the polysaccharide from C. licheniforme resembles that from A. cylindrica in having terminal mannosyl residues as side branches (absent from A. variabilis). The polysaccharides from A. variabilis resemble that from A. cylindrica in having glucose-containing side branches (absent from the heterocyst polysaccharide from C. licheniforme), but in contrast to the polysaccharides from the other two species they also have terminal arabinosyl residues as side branches. All of the polysaccharides mentioned appear to be structurally related; we present tentative structures for those not previously investigated. In contrast, the envelope of spores of C. licheniforme contains only a largely 4-linked galactan. The bulk of this envelope is not polysaccharide in nature, and contains aromatic groups.