培养条件下发菜的形态建成

固体培养基培养的发菜(Nostoc flagelliforme)在黑暗与低光强(2·s)条件下细胞发育受到抑制,在光强10、20、30、60 μmol/m2·s 条件下细胞生长良好, 但在60 μmol/m2·s 条件下藻丝体易变黄; 液体充气培养的发菜在光强20、60、180 μmol/m2·s 条件下生长速率、类胡萝卜素与多糖含量均随光强升高而增加。发菜在低营养水平时形成的异形胞较多, 异形胞的发生位置也多样, 有端生、间生和连生。当琼脂浓度为0.5%—4%时发菜具有相同的形态发育特征, 从藻殖段发育至丝状聚集体状态, 再从聚集体中释放藻丝; 当琼脂浓度为6%—8%时发菜发育至丝状聚集体状态, 藻丝包裹在厚胶鞘中, 观察不到藻丝和藻殖段的释放。以上结果表明光照和培养基的含水量对发菜细胞发育具有重要影响。       

PHOTOSYNTHETIC BICARBONATE UTILIZATION BY A TERRESTRIAL CYANOBACTERIUM, NOSTOC FLAGELLIFORME (CYANOPHYCEAE)

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme , after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis–pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na ⁺ -free and Na ⁺ + Li ⁺ media but were not affected by the absence of Cl ⁻ , implying that the bicarbonate uptake was associated with Na ⁺ / HCO₃ ⁻ symport rather than Cl ⁻ /HCO₃ ⁻ exchange system.     

培养条件下发菜细胞超微结构的观察

通过观察发菜(Nostoc flagelliforme Born.et Flah.)细胞在不同生长条件的超微结构,探讨细胞的生长和发育特点以及胶质鞘的形成规律。在蒸馏水中浸泡2h后,各种细胞代谢活跃,能进行正常的生长和分裂,其中营养细胞的细胞壁以及一特殊类型的大细胞与胶质鞘的形成有关。在pH7.0的培养液中,出现与胶质鞘有关的细胞结构。在酸性培养液中未见这些结构。在不合适的pH条件下,一特殊类型的小细胞大量增殖。     

EFFECTS OF POTASSIUM ON THE PHOTOSYNTHETIC RECOVERY OF THE TERRESTRIAL CYANOBACTERIUM,NOSTOC FLAGELLIFORME (CYANOPHYCEAE) DURING REHYDRATION1

Effects of potassium on the photosynthetic recovery of Nostoc flagelliforme (Berk. & Curtis) Bornet & Flahault were investigated to determine its exact role during rehydration. Potassium enhanced recovery of the ability to reduce the primary quinone‐type acceptor (Q_A) and plastoquinone (PQ) pool and the area over the fluorescence rise curve was increased by 127%. The proportions of closed PSII reaction centers at phases J and I and the net rate of closure of PSII reaction centers were decreased by, respectively, 19%, 8%, and 23% with the addition of potassium, due to changes in the ability of PSII for multiple turnovers needed to reduce the PQ pool. Potassium significantly enhanced the probability of electron transfer beyond Q_A and the recovery of electron transport flux per PSII reaction center. Electron transport from water to methyl viologen for samples rehydrated in K⁺‐free BG₁₁ medium was 54% of those with the addition of potassium. However, electron flow from water to p‐benzoquinone and from reduced 2,6‐dichlorophenol‐indophenol to methyl viologen showed little change with the addition of potassium. The fast phase and slow phase of millisecond delayed light emission and the ATP content for samples rehydrated in K⁺‐free BG₁₁ medium were, respectively, 71.6%, 50.7%, and 77.1% of those with the addition of potassium. These suggested that potassium affected electron transfer from PQ to plastocyanin through the cytochrome b₆f complex and the proton motive force across the thylakoid membranes, probably reflecting its role in charge balance during H⁺ transport by the cytochrome b₆f complex.     

PHOTOSYNTHETIC INSENSITIVITY OF THE TERRESTRIAL CYANOBACTERIUM NOSTOC FLAGELLIFORME TO SOLAR UV RADIATION WHILE REHYDRATED OR DESICCATED1

Photosynthetic performance of the terrestrial cyanobacterium Nostoc flagelliforme (M. J. Berkeley et M. A. Curtis) Bornet et Flahault during rehydration and desiccation has been previously characterized, but little is known about the effects of solar UV radiation (280–400 nm) on this species. We investigated the photochemical activity during rehydration and subsequent desiccation while exposing the filamentous colonies to different solar radiation treatments. Photochemical activity could be reactivated by rehydration under full‐spectrum solar radiation, the species being insensitive to both ultraviolet‐A radiation (UVAR; 315–400 nm) and ultraviolet‐B radiation (UVBR). When the rehydrated colonies were exposed for desiccation, the effective PSII photochemical yield was inhibited by visible radiation (PAR) at the initial stage of water loss, then increased with further decrease in water content, and reached its highest value at the water content of 10%–30%. However, no significant difference was observed among the radiation treatments except for the moment when they were desiccated to critical water content of about 2%–3%. At such a critical water content, significant reduction by UVBR of the effective quantum yield was observed in the colonies that were previously rehydrated under indoor light [without ultraviolet radiation (UVR)], but not in those reactivated under scattered or direct solar radiation (with UVR), indicating that preexposure to UVR during rehydration led to higher resistance to UVR during desiccation. The photosynthetic CO₂ uptake by the desiccated colonies was enhanced by elevation of CO₂ but was not affected by both UVAR and UVBR. It increased with enhanced desiccation to reach the maximal values at water content of 40%–50%. The UV‐absorbing compounds and the colony sheath were suggested to play an important role in screening harmful UVR.     

AUTOINHIBITION OF SPORE GERMINATION IN NOSTOC SPONGIAEFORME (CYANOPHYCEAE)1

Medium in which cultures of Nostoc spongiaeforme Ag. have sporulated contains one or more substances which inhbit the germination of spores (akinetes) of this organism. Germination of spores occurs rapidly in the absence of these substances, but is virtually completely suppressed in their presence.     

POTASSIUM ALLEVIATES THE INHIBITORY ACTION OF AMMONIUM UPON THE PHOTOSYNTHETIC RECOVERY OF NOSTOC FLAGELLIFORME (CYANOPHYCEAE) DURING REHYDRATION1

Effects of ammonium on the photosynthetic recovery of Nostoc flagelliforme Berk. et M. A. Curtis were assayed when being rehydrated in low‐K⁺ or high‐K⁺ medium. Its photosynthetic recovery was K⁺ limited after 3 years of dry storage. The potassium absorption of N. flagelliforme reached the maximum after 3 h rehydration in low‐K⁺ medium but at 5 min in high‐K⁺ medium. The K⁺ content of N. flagelliforme rehydrated in high‐K⁺ medium was much higher than that in low‐K⁺ medium. The maximal PSII quantum yield (F_v/F_m) value of N. flagelliforme decreased significantly when samples were rehydrated in low‐K⁺ medium treated with 5 mM NH₄Cl. However, the treatment of 20 mM NH₄Cl had little effect on its F_v/F_m value in high‐K⁺ medium. The relative F_v/F_m 24 h EC₅₀ (concentration at which 50% inhibition occurred) value of NH₄⁺ in high‐K⁺ medium (64.35 mM) was much higher than that in low‐K⁺ medium (22.17 mM). This finding indicated that high K⁺ could alleviate the inhibitory action of NH₄⁺ upon the photosynthetic recovery of N. flagelliforme during rehydration. In the presence of 10 mM tetraethylammonium chloride (TEACl), the relative F_v/F_m 24 h EC₅₀ value of NH₄⁺ was increased to 46.34 and 70.78 mM, respectively, in low‐K⁺ and high‐K⁺ media. This observation suggested that NH₄⁺ entered into N. flagelliforme cells via the K⁺ channel. Furthermore, NH₄⁺ could decrease K⁺ absorption in high‐K⁺ medium.     

OCCURRENCE OF TRI-LAMELLAR BODIES IN ISOLATES OF NOSTOC (CYANOPHYCEAE)1

Tri-lamellar bodies were observed in eight of 29 isolates of Nostoc examined. They appeared identical to the previously described bodies in various species of Anabaena. The bodies consist of three discoid lamellae each ca. 0.3 μm diam and 8 nm thick. The outer lamella (closest to the plasma membrane) is separated from the middle lamella by a 12 nm space whereas the middle and inner lamellae are ca. 8 nm apart. Osmiophilic striations 3 nm wide were generally observed running between the lamellae. Osmiophilic β granules were usually associated with the inner lamella. The bodies were most always located close to the plasma membrane along the longitudinal wall near the junction of the cross and longitudinal walls. In three isolates the bodies located near the cross walls were associated with gas vesicles and possessed a slightly different morphology. These tri-lamellar bodies consisted of three discoid lamellae, each ca. 2 nm thick, ca. 25 nm apart with electron dense material between the inner and middle lamellae. Pores 20 nm diam and ca. 60 nm apart were observed in layer 2 of the cell wall adjacent to the tri-lamellar bodies. These wall pores were also observed in isolates lacking tri-lamellar bodies.     

RELATIONSHIP OF GROWTH AND PHOTOSYNTHESIS WITH COLONY SIZE IN AN EDIBLE CYANOBACTERIUM,GE‐XIAN‐MI NOSTOC (CYANOPHYCEAE)1

Growth and photosynthesis of an edible cyanobacterium, Ge‐Xian‐Mi (Nostoc), were investigated with differently sized colonies. Both photosynthesis and growth were dependent on the colony size. Compared with larger ones, smaller colonies grew faster regardless of the levels of light and temperature for culture and showed higher values of maximal net photosynthetic rate, apparent quantum yield, light‐saturating and compensating points, and dark respiration. The ratios of chl a content and mass to surface area of a colony increased and that of chl a to mass or mass to volume of a colony decreased with increased colonial sizes. A Ge‐Xian‐Mi colony appeared to increase its chl a content per surface area, enhancing the light‐shading effect; however, at the same time it decreased its mass density on a volume basis, minimizing the enhanced effects of shading and diffusion barrier caused by the thickening outer layer with increasing colony size during growth.     

LIGHT DEPENDENCY OF PHOTOSYNTHETIC RECOVERY DURING WETTING AND THE ACCLIMATION OF PHOTOSYNTHETIC APPARATUS TO LIGHT FLUCTUATION IN A TERRESTRIAL CYANOBACTERIUM NOSTOC COMMUNE1

The PSII photochemical activity in a terrestrial cyanobacterium Nostoc commune Vaucher ex Bornet et Flahault during rewetting was undetectable in the dark but was immediately recognized in the light. The maximum quantum yield of PSII (F_v/F_m) during rewetting in the light rose to 85% of the maximum within ～30 min and slowly reached the maximum within 6 h, while with rewetting in the darkness for 6 h and then exposure to light the recovery of F_v/F_m required only ～3 min. These results suggested that recovery of photochemical activity might depend on two processes, light dependence and light independence, and the activation of photosynthetic recovery in the initial phase was severely light dependent. The inhibitor experiments showed that the recovery of F_v/F_m was not affected by chloramphenicol (CMP), but severely inhibited by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) in the light, suggesting that the light‐dependent recovery of photochemical activity did not require de novo protein synthesis but required activation of PSII associated with electron flow to plastoquinone. Furthermore, the test indicated that the lower light intensity and the red light were of benefit to its activation of photochemical activity. In an outdoor experiment of diurnal changes of photochemical activity, our results showed that PSII photochemical activity was sensitive to light fluctuation, and the nonphotochemical quenching (NPQ) was rapidly enhanced at noon. Furthermore, the test suggested that the repair of PSII by de novo protein synthesis played an important role in the acclimation of photosynthetic apparatus to high light, and the heavily cloudy day was more beneficial for maintaining high photochemical activity.     

CYTOCHROME c548 IN NOSTOC SP. (CYANOPHYCEAE): AN ELECTRON ACCEPTOR FROM REDUCED NADP IN THE DARK1

A c-type, carbon monoxide-binding cytochrome was isolated and studied from an endophytic Nostoc sp. Enzymatic transfer of electrons from NADPH to this cytochrome was demonstrated in cell-free preparations under dark, anaerobic conditions, probably mediated by NADPH-cytochrome reductase or ferredoxin-NADP reductase present in the extracts. This cytochrome, with an α-peak at 548 nm, had physicochemical properties similar to the low potential c-type cytochrome, cytochrome c₅₄₉, previously described by other workers from Anacystis nidulans. The participation of such c-cytochromes in dark electron transport, possibly respiratory, of bluegreen algae is strongly indicated.     

INVOLVEMENT OF MICROCYSTINS AND COLONY SIZE IN THE BENTHIC RECRUITMENT OF THE CYANOBACTERIUM MICROCYSTIS (CYANOPHYCEAE)1

The benthic recruitment of Microcystis was simulated in vitro in order to characterize the colonies of Microcystis recruited and to study the impact of intracellular and extracellular microcystins (MCs), and the influence of colony size on the recruitment process. We observed recruitment dynamics consisting of a lag phase followed by a peak and then a return to low recruitment rates, mainly controlled by passive resuspension throughout the experiment, and by physiological processes during the recruitment peak. Ninety‐seven percent of the Microcystis colonies recruited were <160 μm in maximum length, and their cells contained much greater amounts of MCs (0.26 ± 0.14 pg eq microcystin leucine‐arginine variant [MC‐LR] · cell^?1) than those in benthic colonies (0.021 ± 0.004 pg eq MC‐LR · cell^?1). The MC content of recruited Microcystis varied significantly over time and was not related to changes in the proportion of potentially toxic genotypes, determined using real‐time PCR. On the other hand, the changes in MC content in the potentially toxic Microcystis recruited were closely and negatively correlated with recruitment dynamics; the lowest MC contents corresponded to high recruitment rates, and the highest MC contents corresponded to low recruitment rates. Thus, depending on temperature and light conditions, these variations are thought to result from the selection of various subpopulations from among the smallest and the most toxic of the initial benthic population. Adding purified MC‐LR to experimental treatments led to a decreased recruitment of Microcystis and more specifically of mcyB genotypes.     

SODIUM DEPRIVATION UNDER ALKALINE CONDITIONS CAUSES RAPID DEATH OF THE FILAMENTOUS CYANOBACTERIUM SPIRULINA PLATENSIS1

Like other alkaliphiles, the cyanobacterium Spirulina platensis (Norst.) Geitler requires sodium to function properly at elevated pH values. At pH 10.0, 150–250 mM Na⁺ were required for optimal growth, whereas 2.5 mM were sufficient for short-term photosynthetic oxygen evolution. The complete absence of sodium, however, caused S. platensis to deteriorate. O₂ evolution stopped, the absorbance at 620 nm corresponding to phycocyanin decreased, and the cells lysed within 1 h, a process accelerated by light. The activity of photosystem II, but not that of photosystem I, was affected in the process, which was irreversible unless sodium was readded within 15 minfrom the onset of the deprivation. The effect was mimicked, even in the presence of sodium, by the ionophore nigericin. We suggest that the cascade of events leading to cell lysis is primarily due to the inability of S. platensis to maintain a proton gradient (acid inside), possibly due to inactivity of a sodium/proton antiporter, as demonstrated for other alkaliphiles.     

多变鱼腥藻半稳定状态连续培养的若干特征

分别使用恒化装置和全玻璃发酵罐连续培养多变鱼腥藻。在稳定条件下加以周期性的光照(L∶D=12∶12),经5—6d得到半稳定状态连续培养物。在光照阶段,培养物的生物量增长速度约等于稀释速度D的两倍,叶绿素的增长速度略小于D的两倍,糖原的累积速度几乎高出D~5的一个数量级。细胞内糖原和蛋白质含量变化的时间过程反映出培养物在光-暗条件下的碳氮物质合成与消耗相互联系的代谢特点。半稳定状态连续培养受培养物内在的生理活性支配,生长参数的变化符合方程X=X_(oe)~((μ-D)~t),但不同于恒浊培养和恒化培养。外界因素的强弱变化只改变生长参量变化的强度。本法适用于研究微藻的生态生理。     

INTERACTION OF PLECTONEMA BORYANUM (CYANOPHYCEAE) AND THE LPP-CYANOPHAGES IN CONTINUOUS CULTURE1

Continuous culture techniques are used to study long-term population interactions between Plectonema boryanum Gomont, a filamentous bluegreen alga, and the LPP-viruses which infect it. After LPP-I (virulent cyanophage) infection of sensitive algae, 3 oscillations occur in cell density with concomitant oscillations in virus titer before final stabilization of both algal and viral concentrations. After LPP-ID and LPP-2 (temperate viruses) infection, oscillation in cell density occurred with burst of virus particles. Resistant algae always repopulated the chemostat; lysogeny was not established. The interaction between Plectonema that was resistant to virus infection and the 3 LPP-cyanophages resulted in rapid elimination of the viruses from the chemostat in the effluent. When lysogenic P. boryanum was tested, a law population of virus was present in the chemostat throughout the incubation period indicative of spontancous induction. Clones of lysogenic algae were isolated.     

EFFECTS OF CO2 ENRICHMENT ON THE BLOOM‐FORMING CYANOBACTERIUM MICROCYSTIS AERUGINOSA (CYANOPHYCEAE): PHYSIOLOGICAL RESPONSES AND RELATIONSHIPS WITH THE AVAILABILITY OF DISSOLVED INORGANIC CARBON1

Microcystis aeruginosa Kütz. 7820 was cultured at 350 and 700 μL·L ^{? 1} CO₂ to assess the impacts of doubled atmospheric CO₂ concentration on this bloom‐forming cyanobacterium. Doubling of CO₂ concentration in the airflow enhanced its growth by 52%–77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO₂. However, saturating irradiances for photosynthesis and light‐saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO₂ concentration in the airflow had less effect on DIC‐saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO₂ and HCO₃ ^? levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO₂ dissolution into the liquid increased proportionally when CO₂ in air was raised from 350 to 700 μL·L ^{? 1}, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO₂ could enhance CO₂ dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO₃ ^? concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO₂ concentrating mechanism might decrease.     

ISOLATION OF ccmKLMN GENES FROM THE MARINE CYANOBACTERIUM, SYNECHOCOCCUS SP. PCC7002 (CYANOPHYCEAE), AND EVIDENCE THAT CcmM IS ESSENTIAL FOR CARBOXYSOME ASSEMBLY

A high CO₂ requiring mutant of the marine cyanobacterium Synechococcus PCC7002 was generated using a random gene-tagging procedure. This mutant demonstrated a reduced photosynthetic affinity for inorganic carbon (C_i) and accumulated high internal levels of C_i that could not be used for photosynthesis. Analysis of the mutant genomic DNA showed that the mutagenesis had disrupted a cluster of genes involved in the cyanobacterial CO₂ concentrating mechanism (CCM), the so-called ccm genes. These characteristics are consistent with a cyanobacterial mutant with defects in carboxysome assembly and/or functioning. Further genomic analyses indicated that the genes of the Synechococcus PCC7002 operon, ccmKLMN , are structurally similar to those of two closely related cyanobacteria, Synechococcus PCC7942 and Synechocystis PCC6803. The Synechococcus PCC7002 ccmM gene, which encodes a polypeptide with a predicted size of 70 kDa, was the direct target of the mutagenesis event. The CcmM protein has two distinct regions: an N-terminal region that shows similarity to an archaeon gamma carbonic anhydrase and a C-terminal region that contains repeated domains demonstrating sequence similarity to the small subunit of Rubisco. Physiological analysis of a ccmM -defined mutant showed that these cells were essentially identical to the original mutant; they required high CO₂ concentrations for growth, they had a low photosynthetic affinity for C_i, and they internalized C_i to high levels. Moreover, ultrastructural examination showed that both the original and the defined mutants lack carboxysomes. Thus, our results demonstrate that the ccmM gene of Synechococcus PCC7002 encodes a polypeptide that is essential for carboxysome assembly and therefore for proper functioning of the cyanobacterial CCM.     

COMPARATIVE STUDY ON THE PHOTOSYNTHETIC PROPERTIES OF PRASIOLA (CHLOROPHYCEAE) AND NOSTOC (CYANOPHYCEAE) FROM ANTARCTIC AND NON‐ANTARCTIC SITES1

The terrestrial cyanobacterium Nostoc commune Vaucher ex Bornet et Flahault occurs worldwide, including in Japan and on the Antarctic continent. The terrestrial green alga Prasiola crispa (Lightf.) Kütz. is also distributed in Antarctica. These two species need to acclimate to the severe Antarctic climate including low ambient temperature and desiccation under strong light conditions. To clarify this acclimation process, the physiological characteristics of the photosynthetic systems of these two Antarctic terrestrial organisms were assessed. The relative rate of photosynthetic electron flow in N. commune collected in Japan and in Antarctica reached maxima at 900 and 1,100 μmol photons · m^?2 · s^?1, respectively. The difference seemed to reflect the presence of high amounts of UV‐absorbing substances within the Antarctic cyanobacterium. On the other hand, the optimal temperatures for photosynthesis at the two locations were 30°C–35°C and 20°C–25°C, respectively. This finding suggested a decreased photosynthetic thermotolerance in the Antarctic strain. P. crispa exhibited desiccation tolerance and dehydration‐induced quenching of PSII fluorescence. Re‐reduction of the photooxidized PSI reaction center, P700, was also inhibited at fully dry states. Photosynthetic electron flow in P. crispa reached a maximum at 20°C–25°C and at a light intensity of 700 μmol photons ? m^?2 ? s^?1. Interestingly, the osmolarity of P. crispa cells suggested that photosynthesis is performed using water absorbed in a liquid form rather than water absorbed from the air. Overall, these data suggest that these two species have acclimated to optimally photosynthesize under conditions of the highest light intensity and the highest temperature for their habitat in Antarctica.     

DEVELOPMENT OF THE FLAGELLAR APPARATUS AND FLAGELLAR ORIENTATION IN THE COLONIAL GREEN ALGA GONIUM PECTORALE (VOLVOCALES)1

Vegetative cells of Gonium pectorale have a fine structure similar to that of Chlamydomonas. In addition, three zones comprise an extracellular matrix; a fibrillar sheath and tripartite boundary surround individual cells, and a fragile capsule zone surrounds the entire colony. Cytokinesis is accomplished by a phycoplast and cleavage furrow. The flagellar apparatus of the immature vegetative cell of this colonial alga is similar to that of Chlamydomonas, but the basal bodies are slightly separated at their proximal ends. The four microtubular rootlets alternate between two and four members. During development, the basal bodies become further separated and nearly parallel. The distal fiber is stretched, but it remains attached to both basal bodies. At maturity, the basal bodies of peripheral cells of the colony have rotated in opposite directions on their longitudinal axes resulting in a displacement of the distal fiber to one side, an asymmetrical orientation of the rootlets and loss of 180° rotational symmetry. Central cells remain similar to Chlamydomonas in that basal bodies do not rotate, rootlets are cruciate, the distal fiber remains medially inserted and 180° rotational symmetry is conserved. A “pin-wheel” configuration of flagellar pairs and the orientation of parallel rootlets toward the colony perimeter probably accounts for the rotation of the colonies during forward swimming. In addition, these ultrastructural features support the traditional placement of G. pectorale as an intermediate between the unicellular Chlamydomonas and the more complex colonial volvocalean genera.     

THE MARINE AND TERRESTRIAL PRASIOLALES (CHLOROPHYTA) OF GALWAY CITY, IRELAND: A MORPHOLOGICAL AND ECOLOGICAL STUDY

Green algae belonging to the order Prasiolales have been reported frequently in terrestrial, freshwater, and marine habitats, generally in situations in which they are not submerged continuously and often in association with deposits of avian feces or other rich sources of nitrogenous compounds. Terrestrial habitats in Galway City on the west coast of Ireland have large populations of four such algae: Rosenvingiella polyrhiza (Rosenvinge) P. C. Silva, Prasiola calophylla (Carmichael ex Greville) Kützing, P. crispa (Lightfoot) Kützing, and P. stipitata Suhr ex Jessen, of which only the last is in any way fully associated with a tidal regime. The other species are found in an extraordinary range of nonmarine terrestrial habitats in the center of Galway, a city that still retains its narrow, medieval street plan. Width of the streets, proportion of residences, substratum type, and aspect are shown to be the main factors affecting the distribution of these algae, although a combination of consistent dampness and nitrogenous-compound availability from animal wastes is likely to be the primary determining factor. Morphological and phenological data are presented for each entity, and it is concluded from field observations that R. polyrhiza should continue to be recognized as a separate entity, even though a close relationship with Schizogonium murale Kützing is probable.