SEXUALITY AND CULTURAL CHARACTERISTICS OF ASPERGILLUS HETEROTHALLICUS

Aspergillus heterothallicus K., F. and R., isolated from Costa Rican soils, represents the first species in this genus that is truly heterothallic. Each of the eleven strains investigated is functionally hermaphroditic but self-sterile and falls into one of two cross-mating classes, A or a. The mating-type factors A and a appear to be an allelic pair segregating independently of the locus for pigmentation of mycelium which varies from yellow to pinkish orange in different isolates. The striking variation in the development of hülle cell masses that occurred among the progeny from the cross WB 5096(A) × WB 5097(a) was found to be genetically controlled. The gene responsible for a delay in the formation and maturation of cleistothecia appeared to be loosely linked to the a mating-type locus and could be recombined into the A mating type. The mechanism of fertilization has not been completely elucidated. Coiled ascogonia were found within young hülle cell masses developed in cultures where two isolates of opposite mating types were crossed; such coils have not been observed, thus far, within hülle cell masses in unmated cultures. Although no recognizable male structure has been found, the fertilizing element appears to be mycelial in form rather than conidial. Interspecific mating did not occur when strains of Aspergillus heterothallicus were paired with other members of the A. nidulans group.     

AKINETE PRODUCTION OF ANABAENA LEMMERMANNII AND A. CYLINDRICA (CYANOPHYCEAE) IN NATURAL POPULATIONS OF N‐ AND P‐LIMITED COASTAL MESOCOSMS1

A strong biomass increase of two Anabaena species was observed in natural plankton community enclosed into nine large mesocosms (51 m³) and manipulated with mineral nutrients and an organic carbon source during a 3‐week period in the coastal Baltic Sea. The water column and settled material from the bottom of the mesocosms were sampled at 2‐day intervals. Planktonic populations of Anabaena lemmermannii Richter and A. cylindrica Lemmermann and sedimentation rates of akinetes to the bottom were quantified. Comparing mesocosms with artificially induced nitrogen and phosphorus limitation, we found that during the third week of the experiment, the population size of A. lemmermannii was clearly higher in nitrogen‐limited units (by a factor of 2.4), whereas the production rate of akinetes was higher in the phosphorus‐limited units (by a factor of 2.5). Input of freshly produced A. lemmermannii akinetes to the benthos was on average 15 × 10⁶ and 6 × 10⁶ cells· m^?2·d^?1 in the P^? and N^? limited mesocosms, respectively. Our estimates of specific akinete production rate of A. lemmermannii in P^? and N^? limited mesocosms revealed an even larger divergence (a factor of 5.5), being on average 2.4 and 0.4 akinetes·10^?3 vegetative cells^?1·d^?1, respectively. The phosphorus addition effectively reduced akinete production of A. lemmermannii. Differences in the nutrient manipulation had no apparent effect on the biomass and akinete production of A. cylindrica. The akinete production pattern of A. cylindrica revealed a 1‐week delay compared with the vegetative population peak, whereas such a delay was not obvious in A. lemmermannii.     

ADJUSTABILITY OF THE CIRCADIAN CLOCK IN THE COCKROACHES: A COMPARATIVE STUDY OF TWO CLOSELY,RELATED SPECIES,BLATTELLA GERMANICA AND BLATTELLA BISIGNATA

A single 2h light pulse (250 lux) was given at various times to phase shift the locomotor circadian rhythm of two species of closely related cockroaches, Blattella bisignata and Blatella germanica. The phase-response curve (PRC) of both species showed a similar pattern. Phase delays and advances were induced by light pulse during the early and late subjective night, respectively, while no clear phase shifting was elicited during the subjective day. However, the magnitude of the phase delay (1.89h ± 0.66h) and advance (0.69h ± 0.36h) of B. bisignata was significantly larger than that of B. germanica (0.78h ± 0.38h and 0.35h ± 0.18h, respectively). This result indicates the superior adjustability of the circadian clock in B. bisignata. The periodresponse curve (PdRC) was also constructed for both species. Although both species did not show great flexibility in circadian period changes, the phase shifts were significantly correlated with the period changes in the advance zone of B. bisignata (r = 0.72, P <. 1). This allowed the circadian clock of B. bisignata to display better entrainability since the phase advance adjustment was significantly more difficult than that of phase delay. The results indicate the overall adjustability of the circadian clock of B. germanica is inferior to that of B. bisignata. The significance of this finding is discussed from an ecological perspective. (Chronobiology International, 18(5), 767– 780, 2001)     

ROLE OF NUTRIENT FLUCTUATIONS AND DELAYED DEVELOPMENT IN GAMETOPHYTE REPRODUCTION BY MACROCYSTIS PYRIFERA (PHAEOPHYCEAE) IN SOUTHERN CALIFORNIA1

Organisms occurring in environments subject to severe disturbance and/or periods of poor environmental quality that result in severe adult mortality can survive these periods by relying on alternate life stages that delay their development in a resistant state until conditions improve. In the northeast Pacific, the forest‐forming giant kelp Macrocystis pyrifera (L.) C. Agardh periodically experiences widespread adult mortality during extended periods of extremely low nutrients and high temperatures, such as those associated with El Niño. Recovery following these periods is hypothesized to occur from microscopic life stages that delay their development until the return of favorable conditions. In the laboratory, we experimentally examined the environmental conditions responsible for regulating delayed development of the microscopic stages of M. pyrifera from Southern California, USA. Nutrients controlled the delay and resumption of gametophyte growth and reproduction, perhaps linked to the large fluctuations in nutrients occurring seasonally and interannually in this region. Although growth of gametophytes proceeded in the virtual absence of nitrate, both nitrate and other trace nutrients were necessary for gametogenesis. Upon exposure to elevated nutrients, delayed gametophytes produced sporophytes more quickly (5–20 d) and at smaller sizes (10–200 μm) than gametophytes that had never been delayed (18–80 d, 80–400 μm, respectively), reducing negative density‐dependent effects. This finding demonstrates that delayed gametophytes of M. pyrifera rapidly utilize increased resources to consistently produce sporophytes. Further work is needed to assess their potential role in population recovery following periods of poor environmental quality.     

GEOGRAPHIC VARIATION AND HETEROCHRONY IN TWO SPECIES OF COWRIES (GENUS CYPRAEA)

Geographic variation in the marine, Indo-Pacific cowry, Cypraea caputserpentis, involves clinal variations that parallel the ontogenetic development of adult shell characteristics. Cypraea caputdraconis, a closely related species endemic to Easter Island and Sala y Gómez, is morphologically similar to juvenile C. caputserpentis. Using multivariate measures of size and shape, I examine these patterns as a possible outcome of heterochrony, or changes in the timing of developmental events in ontogeny. Whorl-expansion rates of juvenile shells are significantly higher in C. caputdraconis when compared to C. caputserpentis and are negatively correlated with surface seawater temperatures among populations of C caputserpentis. High expansion rates, often associated with slow growth, result in a delay in the onset of lateral callus development and subsequent paedomorphosis. Ontogenetic trajectories calculated from growth series of adult and preadult shells indicate that paedomorphosis results from the combined effects of neoteny and post-displacement. Paedomorphosis among cowries may result from the advantages of larger body size relative to shell size under reduced predation intensities and associated increases in fecundity.     

EFFECTS OF RESIDUAL TOOTHPASTE FLAVOR ON FLAVOR PROFILES OF COMMON FOODS AND BEVERAGES

Because toothpaste and other menthol/surfactant‐containing products have residual effects, researchers should ensure that enough time has elapsed between use of toothpaste and evaluation of food products. In this study, orange juice, coffee, sausage and processed cheese were profiled under controlled conditions and at 4, 12, 30 and 60 min after panelists brushed with a strongly mentholated toothpaste. Residual effects of the toothpaste at 4 min reduced several aromatic attributes, but did not affect most fundamental taste or texture attributes. A mint aromatic was observed in some food products after toothpaste use, even after 12 min. Chemesthetic attributes were diminished when a product was presented within 12 min of brushing. Results suggested that the amount of time needed between brushing and tasting depended on the food product. Orange juice, an acidic beverage, required at least an hour's delay; fatty, solid foods could be tasted almost immediately after toothbrushing if provided a warm‐up sample first.     

REGULATION OF THE 24H BODY TEMPERATURE RHYTHM OF WOMEN IN LUTEAL PHASE: ROLE OF GONADAL STEROIDS AND PROSTAGLANDINS

An investigation into whether the rise in the 24h body temperature rhythm observed in the luteal menstrual phase is antagonized by the administration of prostaglandin synthesis inhibitors has been made. Intravaginal body temperature was monitored continuously for 24 h, once in the follicular and twice in the luteal phase. In the luteal phase, women were studied both without and with the simultaneous administration of a prostaglandin synthesis inhibitor (lysine acetylsalicylate; 1.8 g every 6 h orally). The progesterone/estradiol ratio (measured at 17:00h each day) was related to mesor (r=0.825; P<0.001), acrophase (r=0.682; P<0.02), and amplitude (r=?0.731; P<0.001) of the 24h body temperature rhythm. Luteal phase elevation of the progesterone/estradiol ratio was associated with a 0.32±0.07°C increase in mesor (P<0.01), a 0.11±0.02°C decrease in amplitude (P<0.001), and a 34.8±11.6 min delay in acrophase (P<0.03) of the 24h body temperature rhythm. Prostaglandin synthesis inhibitors did not counteract these modifications. The present data shows that the modifications of the circadian parameters of the 24h body temperature rhythm observed during the luteal phase of the menstrual cycle are strictly related to modifications of the progesterone/estradiol ratio, and presumably independent of prostaglandin synthesis.     

EFFECT OF CHRONIC HYPERPROLACTINEMIA ON DAILY CHANGES OF GLUTAMATE AND ASPARTATE CONCENTRATIONS IN THE MEDIAN EMINENCE AND DIFFERENT HYPOTHALAMIC AREAS OF MALE RATS

The 24h changes of glutamate (GLU) and aspartate (ASP) werestudied in the median eminence (ME) and hypothalamic areas. It was analyzedwhether prolactin may change their daily patterns. The hypothalamic concentrationof these amino acids was measured by high-performance liquid chromatography(HPLC) with fluorometric detection. Plasma prolactin levels increased overthe 24h light-dark cycle after pituitary grafting compared to controls, andits circadian rhythm was disrupted. In controls, aspartate and glutamate inthe hypothalamic areas studied followed a specific daily variation or showedno rhythmicity. In the median eminence, hyperprolactinemia seem to phase advancethe aspartate or glutamate peaks from 16:00 to 12:00. In the mediobasal hypothalamus,hyperprolactinemia altered daily changes of aspartate and significantly decreasedits concentration. Also, it seems to delay the nocturnal glutamate peak comparedto controls. In the posterior hypothalamus, hyperprolactinemia did not changeaspartate and glutamate concentrations and their daily changes, although itincreased the glutamine concentration. These data show the existence of 24hchanges of amino acid concentration in three of the hypothalamic regions studied.Increased plasma prolactin levels differentially affected these patterns dependingon the hypothalamic area analyzed. (ChronobiologyInternational, 17(5), 631–643, 2000)     

STUDIES ON THE FLORAL HISTOGENESIS AND PHYSIOLOGY OF PERILLA. III. EFFECTS OF INDOLEACETIC ACID ON THE FLOWERING OF APICAL BUDS AND EXPLANTS IN CULTURE

Raghavan , V. (Princeton U., Princeton, N. J.) Studies on the floral histogenesis and physiology of Perilla. III. Effects of indoleacetic acid on the flowering of apical buds and explants in culture. Amer. Jour. Bot. 48(10): 870–876. Illus. 1961.—The responses of apical buds and explants of a short-day plant, Perilla frutescens (L.) Britt. var. 'Tall Late,' when grown in vitro in White's medium supplemented with indoleacetic acid (IAA) and subjected to short-days (SD) or long-days (LD), are described. Additions of varying concentrations of IAA to the medium inhibited the flowering of the photoinduced apical buds in 2 ways. There was a progressive delay in the appearance of the first signs at the apex and a gradual transition from the more flower-like structures in lower concentrations of IAA (0.1 mg/liter) to sterile cones in higher doses. The sterile cones had florets with well-developed calyx and corolla lobes, but lacked the sporogenous tissues. When subjected to LD, visible signs were observed only in buds grown in 0.1 and 1.0 mg/liter IAA, the pronounced effect of the auxin being in the step-wise inhibition in the formation of the non-sporogenous tissues of the differentiating florets. Flowering of the explants with the 1st pair of unfolded leaves was also inhibited by IAA in either SD or LD, but the 1st signs appeared relatively faster than in apical buds. When photoinduced, explants with the 1st and 2nd pairs of unfolded leaves flowered in all concentrations of IAA tried (up to 100 mg/liter) while those kept in LD remained entirely vegetative.     

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.     

EFFECTS OF DEXAMETHASONE ON NEUROTRANSMITTER ENZYMES IN CHROMAFFIN TISSUE OF THE NEWBORN RAT

—Dexamethasone administration to newborn rats resulted in an increase in phenylethanolamine N-methyltransferase activity in superior cervical ganglia. The same treatment resulted in a decrease in tyrosine hydroxylase and choline acetyltransferase activities. The decline in choline acetyltransferase activity after dexamethasone treatment was only seen when the drug was given before 5 days of age. When dexamethasone was given to pregnant rats it caused an age-dependent decrease in choline acetyltransferase in the adrenals, superior cervical ganglia and para-aortic chromaffin tissue of the offspring. These results suggest that dexamethasone administration may delay the development of the preganglionic neurons of sympathetic ganglia. This in turn would delay the development of tyrosine hydroxylase but not phenylethanolamine N-methyltransferase.     

DELAYED MATURATION,NEOTENY, AND SOCIAL SYSTEM DIFFERENCES IN TWO MANAKINS OF THE GENUS CHIROXIPHIA

Long-tailed manakins (Chiroxiphia linearis) and swallow-tailed manakins (C. caudata) are closely related, sexually dichromatic, lek-breeding species in which male mating success is highly skewed. Males of both species delay plumage maturation. Before reaching the definitive state, they wear a sequence of feather coats less conspicuous than that of the adult. Nondefinitive plumages probably enhance male survival in the two species; in C. caudata they may also enhance breeding success of young males, who may be fully reproductively mature their first year. In C. linearis testicular development is retarded along with that of plumage, although males may be physiologically capable of breeding prior to the acquisition of the definitive plumage. This difference probably reflects differences in the social systems of the two species. Five hypotheses have been proposed to explain the evolution of delayed plumage maturation. The sexual-selection, cryptic-breeder, and winter-adaptation hypotheses suggest that it functions primarily to enhance survival of young males. The juvenile- and female-mimicry hypotheses emphasize enhancement of immediate mating success. Support is provided for all but the female-mimicry hypothesis; it is argued that data are more consistent with juvenile mimicry and a neotenic origin of nondefinitive plumages.     

EFFECTS OF MICROTUBULE INHIBITORS ON PRONUCLEAR MIGRATION AND EMBRYOGENESIS IN FUCUS DISTICHUS(PHAEOPHYTA)1

Pronuclear migration in Fucus distichus spp. edentatus (de la Pyl.) Powell is blocked by incubation of fertilized eggs in colchicine (1 mg/ml) and Nocodazole (2 μg/ ml). Rhizoids form prior to decondensation of the sperm chromatin in eggs in which pronuclear fusion is blocked. This occurs during continuous colchicine incubation as well as in eggs recovering from a short treatment with either drug following fertilization. During recovery of the cells, the sperm and egg chromosomes condense, and the sperm chromosomes migrate toward the egg pronucleus. The delay in migration following removal of colchicine is as much as 24 h and is even slower following removal of Nocodazole. The egg chromosomes form a metaphase plate in treated cells while the sperm chromosomes are still distant in the cytoplasm. This suggests that egg centrioles are important in the mitotic division of the zygote, not sperm centrioles. The effect of colchicine treatment on the mitotic plane and cytokinesis is also discussed.     

CALCIUM MOVEMENT,GRAVIRESPONSIVENESS, AND THE STRUCTURE OF COLUMELLA CELLS IN PRIMARY ROOTS OF AMYLOMAIZE MUTANTS OF ZEA MAYS

Primary roots of Zea mays cv. Amylomaize were less graviresponsive than primary roots of the wild-type Calumet cultivar. There were no significant differences in: 1) the partitioning of volume to organelles in columella cells, 2) the size or density of amyloplasts, or 3) rates and overall patterns of organelle redistribution in horizontally-oriented roots of the two cultivars. Amyloplasts and nuclei were the only organelles whose movement correlated positively with the onset of root gravicurvature. However, the onset of gravicurvature was not directly proportional to the average sedimentation rate of amyloplasts, since amyloplasts sedimented at equal rates in columella cells of both cultivars despite their differences in root gravicurvature. The more graviresponsive roots of Calumet seedlings were characterized by a more strongly polar movement of ⁴⁵Ca²⁺ from the upper to lower sides of their root tips than the less graviresponsive roots of Amylomaize seedlings. These results suggest that the decreased graviresponsiveness of horizontally-oriented roots of Amylomaize seedlings may be due to a delay in or decreased ability for polar transport of calcium rather than to smaller, more slowly sedimenting amyloplasts as has been suggested for their less graviresponsive coleoptiles.     

PARALLEL EVOLUTION OF LOCAL ADAPTATION AND REPRODUCTIVE ISOLATION IN THE FACE OF GENE FLOW

Parallel evolution of similar phenotypes provides strong evidence for the operation of natural selection. Where these phenotypes contribute to reproductive isolation, they further support a role for divergent, habitat‐associated selection in speciation. However, the observation of pairs of divergent ecotypes currently occupying contrasting habitats in distinct geographical regions is not sufficient to infer parallel origins. Here we show striking parallel phenotypic divergence between populations of the rocky‐shore gastropod, Littorina saxatilis, occupying contrasting habitats exposed to either wave action or crab predation. This divergence is associated with barriers to gene exchange but, nevertheless, genetic variation is more strongly structured by geography than by ecotype. Using approximate Bayesian analysis of sequence data and amplified fragment length polymorphism markers, we show that the ecotypes are likely to have arisen in the face of continuous gene flow and that the demographic separation of ecotypes has occurred in parallel at both regional and local scales. Parameter estimates suggest a long delay between colonization of a locality and ecotype formation, perhaps because the postglacial spread of crab populations was slower than the spread of snails. Adaptive differentiation may not be fully genetically independent despite being demographically parallel. These results provide new insight into a major model of ecologically driven speciation.     

CIRCADIAN PACEMAKER FUNCTION AND ENTRAINMENT DURING MATURATION OF TRANSGENIC HYPERTENSIVE TGR(mREN2)27 AND SPRAGUE-DAWLEY RATS

TGR(mREN2)27 (TGR) transgenic rats develop hypertension due to the mouse mRen-2 gene inserted in their genome. At 5 weeks of age, the blood pressure of TGR rats starts rising, until a maximum is reached at 10 weeks of age. Adult TGR rats show peak values of blood pressure (BP) during the light phase, while heart rate (HR) and motor activity (MA) peak at night. In the present experiment, we evaluated the evolution of circadian rhythms in motor activity, heart rate, and blood pressure of TGR and Sprague-Dawley (SD) rats under 12h light-dark cycles (LD 12:12). Results confirmed that the blood pressure of TGR rats starts to increase at 5 weeks of age, reaching a plateau by the 11th week. Parallel to the increase in blood pressure levels, there was a decrease in the period length of the blood pressure rhythm, a delay in the onset of the alpha phase of the blood pressure rhythm with respect to that of motor activity and heart rate, and a decrease in heart rate levels. In all of the variables studied, the alpha phase of SD rats always started before darkness, whereas that of TGR rats started after lights off. In general, heart rate and motor activity levels of TGR rats were higher than those of SD rats. The amplitude of the circadian rhythms studied was greater in TGR rats than in SD rats. The present results suggest that the different evolution of circadian rhythms in TGR and SD rats might be due to differences in the functioning of the entrainment pathway or the circadian clock itself, which can be detected in young rats and that are probably caused by the expression of the mouse transgene. (Chronobiology International, 18(4), 627–640, 2001)     

INSECTICIDES: THEIR ROUTE OF ENTRY, MECHANISM OF TRANSPORT AND MODE OF ACTION

(1) The assumption that the circulatory system of the insect is instrumental in transporting insecticides to their site of action appeared not to be based on good evidence. On the contrary, experiments specifically designed to test the hypothesis provided ample evidence to refute the idea. Salient points to disprove the haemolymph route of entry can be summed up as follows: (a) A topically applied dose of insecticide does not readily penetrate the insect and the minor fraction that does so is largely retained in the body wall. The small amount that actually passes into the blood is too small to cause symptoms of toxicity if injected into the haemocoel. (b) The amount of insecticide present in the haemolymph (and CNS) does not appear to have any bearing on toxicity - internally introduced insecticides are, in fact, basically very much less toxic than those externally applied. Where injected doses appear to be more toxic than equal amounts topically applied, this is due to the boosting effect of organic solvent carriers. Tests with parabiotically joined insects provide support for the view that haemolymph-borne insecticide is of no consequence. (c) The topographical proximity of the locus of external application with the site of action (the thoracic ganglia) seems to be important irrespective of the general direction of the blood flow, and this should not be so if the circulatory system was instrumental in the transport of insecticide. (d) The introduction into the haemocoel of material such as olive oil, which is an excellent absorbent for insecticides, does not affect the toxicity (speed of action) of externally applied compounds to a significant extent. It should have a pronounced effect if haemolymph-borne insecticide were an essential element in the process of poisoning. (e) As judged by speed of action, blocking of the blood circulation does not hamper the insecticide's movement to the site of action. (2) Only two other feasible routes remain. (a) The insecticide might reach the CNS via peripheral nerves and nerve cord, but the results of histochemical assays of cholinesterase inhibition in the insect's CNS make the idea improbable for organo-phosphates. The nerve route is also incompatible with the observation that a wax barrier blocked the movement in and over the body wall so as to delay the onset of symptoms of toxicity, as such a barrier would not hinder movement into lateral nerves near the locus of application. (6) The only other feasible alternative, i.e. entry by means of lateral transport via the integument of the body wall and tracheae, is supported by autoradiographic and other evidence which showed the insecticide to accumulate in the tracheal system. It is further supported by the fact that inter-tracheal introduction is faster acting than topical treatment, indicating that the tracheal system offers a very effective pathway to the internal organs. (3) Regarding the mechanism of entry, earlier reviews and text books maintain this to be associated exclusively with penetration into and through the integument by a physicochemical process. However, there is good evidence to show that an active process (requiring metabolic activity as the driving force) plays an essential part in lateral movement in the integument - the epidermis, being the only living tissue continuous throughout the general integument, must perform this function. (4) As to the mode of action, the new hypothesis expounded here implies a single mode based on the fact that insecticides cause the extrusion of fluid from the epidermis into the cuticle and beyond, fluid lost from the epidermal cell layer being replaced from haemolymph and internal tissues. The precise mechanism is not clear but could conceivably involve an as yet hypothetical local endocrine system designed to keep the water content in the integument within certain limits. It is suggested that water extrusion affects the integument's permeability to respiratory gases, resulting in a rate of respiration not commensurate with metabolic need, and that the insecticide's arrival in the trachea (tracheoles) of the CNS leads to excitation and knockdown. Death is thought most likely to be due to dehydration of the CNS and subsequent histological degeneration.     

INFLUENCE OF GROWTH STATUS AND NUTRIENTS ON EXTRACELLULAR POLYSACCHARIDE SYNTHESIS BY THE SOIL ALGA CHLAMYDOMONAS MEXICANA (CHLOROPHYCEAE)1

Increased levels of nitrogen in liquid growth medium bring about increased growth and a delay in extracellular polysaccharide production by Chlamydomonas mexicana Lewin on a per-cell basis. Addition of nitrogen to stationary phase cultures causes renewed growth and a temporary lag in polysaccharide synthesis until growth again ceases. Removal of nitrogen terminates growth, causing an immediate increase in polysaccharide synthesis. Phosphate-starved cells show a response similar to nitrogen-starved cells, indicating that the beginning of stationary phase and not nitrogen depletion causes the stimulation in extracellular polysaccharide synthesis. As similar results are assumed to occur on soil, the significance of this response is discussed.     

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.     

FORMATION OF A SUPPLEMENTAL LONG TIME-CONSTANT RESERVOIR OF HIGH ENERGY PHOSPHATE BY BRAIN IN VIVO AND IN VITRO AND ITS REVERSIBLE DEPLETION BY POTASSIUM DEPOLARIZATION

—Brains of mice fed a diet containing 1% cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) accumulated the high energy phosphate compound cyclocreatine-P (1-carboxymethyl-2-imino-3-phosphonoimidazolidine), an analogue of creatine-P (phosphocreatine). During a 50-day feeding period mouse brain cyclocreatine-P increased linearly to 14 μmol/g fresh wt; during this time the total phosphagen level of brain, creatine-P plus cyclocreatine-P, increased from 3 to 15 μmol/g. When the blood-brain barrier was circumvented, a more rapid accumulation of synthetic phosphagen was achieved. Minced brain preparations from 11 to 15-day chick embryos incubated in vitro with 30 mm -cyclocreatine accumulated 10 μmol/g of cyclocreatine-P in 90 min, and this novel high energy phosphate pool could be depleted by incubation with 105 mm -potassium ions or 3 μm -valinomycin. Subsequent regeneration of the depleted pools could also be demonstrated. Brain tissue containing a supplemental reservoir of cyclocreatine-P, which is utilized to regenerate ATP much more slowly than creatine-P, might be better able to withstand anoxia and certain other metabolic stresses, but this has not been established. However, the marked delay of onset of rigor previously shown to occur in ischemic heart and skeletal muscle of cyclocreatine-fed animals is compatible with this suggestion.