Relationship between current velocity,depth and the invertebrate community in a stable river system

The relationship between invertebrate densities, current velocity and water depth was studied in the Dan River, northern Israel. Maximum current preferences ranged from 5–120 cm sec^–1, and depth preferences ranged from 5–60 cm. Thirty-five taxa of invertebrates were collected by means of colonization cages. Larval and adult stages of 3 Elmidae (Coleoptera) species were treated separately: Limnius letourneuxi, Grouvellinus caucasicus and Elmis rioloides. Differences in current preference were observed between larval and adult stages of the same species of Elmidae. Taxa were also grouped according to preference for turbulence. Wide ranges of depth and current velocity preferences were observed. Most of the taxa were found at between 80–100 cm sec^–1 and at depths of less than 30 cm. A correlation between species diversity and current velocity was established. Velocities of 60–80 cm sec^–1 contained the greatest overlap of faunal preference. The sensitivity of selected species to stream flow reduction is discussed.IES Laboratory, Department of Zoology, Hebrew University; and the Nature Reserves Authority     

Effect of relative water motion on photosynthetic rate of red alga Gracitaria conferta

Bulk water velocities and local relative velocities generated in experimental tanks around and within thalli of free moving Gracilaria conferta were estimated according to the dissolution rate of benzoic acid sticks. Boundary-layer thickness and HCO ₃ ^– -mass-transfer coefficient were derived from the water velocities. Average relative velocities varied between 12 cm s ^–1 to less than 0.1 cm s ^–1 as a function of the absolute water flow in the tank, alga shape and location within the thallus. The lower range of velocities was observed at 20% of maximum aeration in the inner part of the plant. In laboratory experiments, photosynthetic rates, as determined in a closed Clark-type O₂-electrode system, increased by 30%–50% when water velocity was increased from zero to about 1.5 cm s ^–1. Another minor increase was obtained between 1.5 cm s ^–1 and 8 cm s ^–1 water velocity. This response to water motion was affected by bulk inorganic carbon concentration and by plant condition, as was reflected from the differences in the response in the winter and spring. It might be suggested that under carbon saturation, water velocity above 2 cm s^–1 provided almost sufficient flow to saturate carbon uptake.     

Study on biomass circulation and gasification performance in a clapboard-type internal circulating fluidized bed gasifier

We investigated the solid particle flow characteristics and biomass gasification in a clapboard-type internal circulating fluidized bed reactor. The effect of fluidization velocity on particle circulation rate and pressure distribution in the bed showed that fluidization velocities in the high and low velocity zones were the main operational parameters controlling particle circulation. The maximum internal circulation rates in the low velocity zone came almost within the range of velocities in the high velocity zone, when u_H/u_mf = 2.2–2.4 for rice husk and u_H/u_mf = 3.5–4.5 for quartz sand. In the gasification experiment, the air equvalence ratio (ER) was the main controlling parameter. Rice husk gasification gas had a maximum heating value of around 5000 kJ/m³ when ER = 0.22–0.26, and sawdust gasification gas reached around 6000–6500 kJ/m³ when ER = 0.175–0.24. The gasification efficiency of rice husk reached a maximum of 77% at ER = 0.28, while the gasification efficiency of sawdust reached a maximum of 81% at ER = 0.25.     

The effect of water flow on photosynthetic processes of the alga Ulva lactuca L.

Photosynthetic rates of aquatic macrophytes are affected by the diffusion of carbon through the boundary layer which decreases with increasing flow velocities. This is shown by a significant increase in photosynthetic rates of Ulva lactuca fronds exposed to friction velocities (u _*) between 0.0 and 0.3 cm s^–1. No further increase in photosynthetic rates is observed at u _* values between 0.3 and 1.0 cm s^–1. Stagnating flow conditions at saturating light levels caused a 29% reduction in photosynthetic rates. Experiments in a closed system indicate that Ulva may utilize internal carbon sources during periods of stagnation. On a subtidal rock directly exposed to wave action, Ulva lactuca is not exposed to such conditions while in a wave flushed intertidal pool stagnation occurs during very short time intervals based on in situ measurements of u _* levels on fronds of this species using a microprocessor-controlled, autonomous recorder and hot-film sensors.     

Avoiding the flow: refuges expand the swimming potential of coral reef fishes

While many coral reef fishes utilise substratum refuges, the direct influence of water flow and swimming ability on such refuging patterns is yet to be established. This study examined the swimming ability and refuging behaviour of a labrid (Halichoeres margaritaceus) and a pomacentrid (Pomacentrus chrysurus) that inhabit high flow, wave-swept coral reef flats. Field observations of refuging patterns were combined with experimental evaluations in a flow tank using a replica of a substratum hole frequently used by these species. Under a range of flow speeds commonly found on the reef flat (0–60 cm s⁻¹), flow within the substratum refuge was reduced to speeds of 0–12 cm s⁻¹, representing a 75–100% flow reduction. Swimming ability of each species was then tested at 60 cm s⁻¹ with and without access to this flow refuge. Both species were able to maintain activity within the 60 cm s⁻¹ flow for considerably longer when provided with a refuge, with increases from approximately 39 min to 36 h for H. margaritaceus and 8 min to 88 h for P. chrysurus. Despite H. margaritaceus having the strongest swimming ability without access to a refuge, P. chrysurus was able to maintain swimming activity more than twice as long as H. margaritaceus when provided with a refuge. These increases in activity are probably due to energetic savings, with this type of refuge providing an estimated 95% energy saving over swimming directly into a unidirectional flow of 60 cm s⁻¹. These results highlight the major advantages provided by refuging behaviour and emphasise the importance of habitat refuges in shaping patterns of habitat use in reef fishes.     

Ion and sugar permeabilities of lecithin bilayers: Comparison of curved and planar bilayers

Summary Na⁺ and sugar permeabilities of egg lecithin bilayers were measured using curved bilayers and planar bilayers as represented by single-bilayer vesicles and black lipid films, respectively. The Na⁺ permeability coefficient measured with single-bilayer vesicles at 25°C is (2.1±0.6)×10^–13 cm sec^–1. Because of technical difficulties it has been impossible to measure ionic permeabilities of values lower than about 10^–10 cm sec^–1 in planar (black) lipid bilayers using tracer methods. Thed-glucose andd-fructose permeabilities were measured with both curved and planar bilayers. The permeability coefficients measured with vesicles at 25°C are (0.3±0.2)×10^–10 cm sec^–1 for glucose and (4±1)×10^–10 cm sec^–1 ford-fructose; these are in reasonable agreement with the corresponding values obtained for planar (black) lipid bilayers which are (1.1±0.3)×10^–10 cm sec^–1 ford-glucose and (9.3±0.3)×10^–10 cm sec^–1 ford-fructose, respectively.This paper is dedicated to the memory of Walther Wilbrandt,cuius nomini nullum par elogium.     

Interaction effects of flow velocity and oxygen metabolism on nitrification and denitrification in biofilms on submersed macrophytes

Effects of water flow velocityon nitrification, denitrification, andthe metabolism of dissolved oxygen andinorganic carbon in macrophyte-epiphytoncomplexes were investigated in the presentstudy. The metabolic rates were measured inmicrocosms containing shoots of Potamogeton pectinatus L. with epiphyticbiofilms in the light and dark with no flow orwith the flow velocities of 0.03 and 9 cms^–1. Photosynthesis and respirationincreased with increasing water flow velocity.Rates of oxygen respiration were positivelycorrelated to the oxygen concentration of thewater. Nitrification was not significantlyaffected by flow velocity, but nitrificationwas higher in light than in dark at 0.03 cms^–1, but not at 9 cm s^–1.Denitrification was higher in stagnant waterand at 9 cm s^–1 than at 0.03 cm s^–1 inthe absence of oxygen, possibly due to complexeffects of water flow velocity on the supply oforganic matter to the denitrifying bacteria.Denitrification was always inhibited in light,and negatively correlated to the oxygenconcentration in dark. Epiphyticdenitrification occurred only at low oxygenconcentrations in flowing water, whereas instagnant water, denitrification was present inalmost oxygen saturated water. Therefore,because there are little of water movements andhigh oxygen consumption in dense stands ofsubmersed macrophytes, significant rates ofepiphytic denitrification can probably be foundwithin submersed vegetation despite high oxygenconcentrations in the surrounding water. Inconclusion, this study shows that the waterflow and oxygen metabolism within submersedvegetation have minor effects on nitrification,but significantly affect denitrification inbiofilms on submersed macrophytes.     

Effects of copper on algal communities at different current velocities

This study examines the influence of current velocity in the toxiceffect of copper in diatom-dominated biofilms grown in artificial channels.Effects on community structure, algal biomass and photosynthesis (carbonincorporation) caused by 15 g L^–1 of copperwere tested at contrasting (1 and 15 cm s^–1)velocities. Moreover, a possible threshold on the effect of copper on algalbiomass and photosynthesis related to current velocity was examined by usingprogressively increasing current velocity (1 to 50 cms^–1) at 15 g L^–1 Cu.Chlorophyll-a decreased ca. 50% as a result of addition of15 g L^–1 Cu. Chlorophyll decrease occurredearlier at 15 cm s^–1 than at 1 cms^–1 when adding 15 g L^–1Cu. Copper also caused a remarkable decrease in carbon incorporation(from 30 to ca. 50%), which was produced earlier at 15 cms^–1 (three days) than at 1 cms^–1 (seven days). Some taxa were affected by thecombination of copper and current velocity. Both Achnanthesminutissima and Stigeoclonium tenue becomedominant at 15 cm s^–1 in the presence of copper.Significant inhibition of algal growth in 15 g L^–1Cu occurred at low (1 cm s^–1) and highvelocities (50 cm s^–1), but not at intermediatevelocity (20 cm s^–1). The experiments indicatethat current velocity triggers the effect that copper has on diatom-dominatedbiofilms, and that the effect is more remarkable at low and high than atintermediate current velocities.     

Dynamics of intertidal marshes near shallow estuaries in Louisiana

A three-year (1991–1993) field investigation was conducted to quantify the hydrodynamics of intertidal marshes adjacent to tidal channels and shallow bays within two Louisiana coastal regions: (1) the sediment-rich Atchafalaya Basin, and, (2) the sediment-poor Terrebonne Basin with relatively minor riverine inflow. The Terrebonne Basin marsh is regularly inundated and flooding is characterized by sporadic draining interspersed by prolonged flooding events. The maximum water depth on the marsh surface exceeds 50 cm, the flow velocity across marsh surface reaches 10 cm sec^–1, and the sediment deposition rate varies from 10 to 90 g m^–2 per tidal cycle. This rather high sediment deposition rate occurs during winter storms with strong southerly winds. In contrast, the marsh site within the sediment-rich Atchafalaya Basin is irregularly inundated and characterized by sporadic flooding interspersed by prolonged draining. There the marsh flooding depth rarely exceeds 25 cm, the over-marsh flow velocity barely reaches 2.5 cm sec^–1, and the sediment deposition rate ranges from 5 to 50 g m^–2 per tidal cycle. The surprisingly low rate of sediment deposition in a marsh within a sediment-rich region is largely due to the man-made canals that alter the hydrologic regime in the upper reaches of the tidal channel.     

The reaction of larvae of Simulium noelleri (Diptera) to different current velocities

Larvae of Simulium noelleri Friederichs aggregate at high population densities (more than 10² cm^–2) on sluices, dams, and spillways. Experiments were conducted in a laboratory trough to assess the reaction of larvae to different current velocities (velocities ranged from 5–49 cm s^–1). In the lower part of the range of water velocities used, larvae moved a greater distance upstream from where they had been located. Larger larvae always showed a greater tendency to move than did smaller larvae, whatever the velocity. This intraspecific variation in reaction to different current velocities allows the aggregation of larvae of mixed sizes at suitable sites, smaller individuals being occluded by those that are larger.     

Continuous culture with deep seawater of a benthic food diatom Nitzschia sp.

A continuous culture system for a benthic food diatom Nitzschia sp. wasestablished by using properties of high nutrient and clean of deep seawater(DSW). DSW collected from 320 m depth in Muroto City, Japan, was introducedinto a glass-pipe bioreactor (14 cm length, 3 cm diam.) containing glassbeads of 0.5 cm diam. as substrata for the alga, and it was incubated at18°C · 80Em^–2sec^–1 · L:D=14:10. The chlorophyll a yield of benthicdiatoms in a reactor as a unit of surface area of the substratum was only0.001–0.003 g cm^–2 when the flow rate of DSW was 0(batch culture conditions). However, when DSW was supplied continuously to areactor, the yield increased to 1.4 g-chl.a cm^–2 alongwith the increase in flow rate of DSW. Moreover, amounts of chl.a washed outof the system were negligible, 0.0014 to 0.0045%, even though theflow rate of DSW was as much as 25 times h^–1, suggesting thatsloughing of benthic diatoms from the substratum was minimized. Although theyield of diatoms fluctuated significantly at the time that the DSW wascollected, the variation could be minimized by increasing the flow rate ofDSW. These results indicate that the continuous culturing system with DSWsupports the stable and effective mass culture of benthic food diatom.     

Effects of current velocity on development and survival of lingcod,Ophiodon elongatus,embryos

Synopsis The influence of current velocity on the survival and development of lingcod embryos was investigated in the field and laboratory. Examination of egg masses at five lingcod spawning sites indicated that embryo mortalities were high (up to 95%) at low-current sites because of inadequate ventilation and resulting hypoxia. Development of embryos near the center of poorly ventilated egg masses was retarded relative to development of embryos near the periphery. Hatching of embryos from poorly ventilated eggs was protracted; embryos from the interior of egg masses hatched later and were significantly smaller than embryos from eggs near the periphery. Oxygen levels measured in egg masses at low-current velocity sites during tidal flow average 16% air saturation, corresponding to a Median Tolerance Limit (LT₅₀) of about 73 h. Oxygen levels measured in egg masses at high-current velocity sites during slack water average 69% air saturation, a level that did not adversely affect the embryos. Current velocities of 10–15 cm s^–1 were needed to maintain interstitial oxygen levels in egg masses near that of the ambient water. Water movement may be an important stimulus for spawning site selection by lingcod. In areas where tidal currents were weak, spawn deposition occurred in shallow water where waves and vertical tide motion created water movement. In areas where tidal currents were strong, spawns were consistently deposited in deeper water.     

Spawning habitat selection and suitability for Japanese dace, Tribolodon hakonensis

We have investigated the effects of three current velocities and three substrate sizes (gravel to cobble) on the spawning behavior of Japanese dace, Tribolodon hakonensis, in spawning-induction and habitat-selection experiments. In the spawning-induction experiment under laboratory conditions the number of females induced to spawn was significantly fewer at low current velocity (ca. 5 cm s^–1) than at medium (ca. 30 cm s^–1) or high (ca. 50 cm s^–1) current velocity. Females spawned independently of substrate size in the experimental tank, and did not bury their eggs in the substrate bed. In the habitat-selection experiment under field conditions, females selected the substrate microhabitat and spawned more frequently at a site with medium substrate size (very coarse gravel; major axis ca. 40 mm) than at sites with small (fine gravel; ca. 8 mm) or large (cobble; ca. 70 mm) substrate size. We conclude that Japanese dace select spawning sites at least partly on the basis of current velocity and substrate size, which affects the survival rate of eggs.     

Assessing the current related heterogeneity and diversity patterns of benthic diatom communities in a turbid and a clear water river

Benthic diatoms were sampled in two rapids, in a turbid South-Finnish river (R. Keravanjoki, 22 FTU) and a clear water river in eastern Finland (R. Vaikkojoki, 4 FTU), to evaluate the diversity and spatial distribution patterns of diatom communities and especially their relationships to current velocity. In both rapids, epilithic diatoms were sampled in 15 sampling squares within three current velocity classes (10 cm s^–1, 40 cm s^–1 and 100 cm s^–1). The sampling squares had significantly different diatom communities in the three current velocity classes at both sampling sites, however, separation of the communities was much more pronounced in the clear water river (p < 0.001) than in the turbid river (p < 0.05). In the clear water river, communities at the highest velocity were highly different from those at the lower velocities. On the other hand, in the turbid river, communities were more similar at all velocities. Significant (p < 0.05) indicators for highest current velocity in the clear water R. Vaikkojoki were Fragilaria capucina var. gracilis Hustedt, F. capucina var. rumpens Lange-Bertalot and Meridion circulare Agardh. There were no significant indicators for high current velocity in the turbid R. Keravanjoki. Cocconeis placentula Ehr., Cymbella sinuata Gregory and Navicula lanceolata (Agardh) Ehr. were the three most abundant species in the highest velocity. This study showed that diatom community was highly specialized but low in diversity at the highest velocity in the clear water river. This pattern was not seen in the turbid R. Keravanjoki, indicating that the diatom community could withstand at the higher current velocities. In addition, the results show the importance of sampling in a variety of current regimes, particularly in clear water rivers, in order to properly assess the diatom diversity and community of a river section.     

Quantifying fluid and bed dynamics for characterizing benthic physical habitat in large rivers

Sturgeon use benthic habitats in and adjacent to main channels where environmental conditions can include bedload sediment transport and high near‐bed flow velocities. Bed velocity measurements obtained with acoustic Doppler instruments provide a means to assess the concentration and velocity of sediment moving near the streambed, and are thus indicative of the bedload sediment transport rate, the near‐bed flow velocity, and the stability of the substrate. Acoustic assessments of benthic conditions in the Missouri River were conducted at scales ranging from the stream reach to individual bedforms. Reach‐scale results show that spatially‐averaged bed velocities in excess of 0.5 m s⁻¹ frequently occur in the navigation channel. At the local scale, bed velocities are highest near bedform crests, and lowest in the troughs. Low‐velocity zones can persist in areas with extremely high mean bed velocities. Use of these low‐velocity zones may allow sturgeon to make use of portions of the channel where the average conditions near the bed are severe. To obtain bed velocity measurements of the highest possible quality, it is necessary to extract bottom‐track and GPS velocity information from the raw ADCP data files on a ping‐by‐ping basis. However, bed velocity measured from a point can also be estimated using a simplified method that is more easily implemented in the context of routine monitoring. The method requires only the transect distance and direction data displayed in standard ADCP data‐logging software. Bed velocity estimates obtained using this method are usually within 5–10% of estimates obtained from ping‐by‐ping processing.     

Larval habitat preference of the endemic Hawaiian midge,Telmatogeton torrenticola Terry (Telmatogetoninae)

Telmatogeton torrenticola Terry is a large endemic chironomid (lastinstar >20 mm) commonly found in high gradient Hawaiian streams on smoothrock surfaces with torrential, shallow flow and in the splash zones ofwaterfalls. We have quantified benthic water flow in larval habitat in a 50m segment of Kinihapai Stream, Maui using a thermistor-based microcurrentmeter. Under base flow conditions at sites suitable for larval attachment,depth was measured and bottom water velocity measurements were made 2 mmabove populations. Larval densities ranged from 386.9–1178m^–2, habitat bottom water velocities from 13.4–64.2 cms^–1, and water depths from 1.5–50 cm. Bottom velocitiesof sites with zero larvae ranged from 20.8–21.8 cm s^–1with depths from 50 to >160 cm. Larval densities were greatest inareas with high bottom water velocities and shallow depths. Stepwisemultiple regression analyses showed that density could be confidentlypredicted best by Froude number (r=0.81; p=0.008). In the absence of Froudenumber as a regression term, the best variable to predict larval density wasbottom velocity ratio: relative depth ratio (r=0.75; p=0.019). In addition,the torrential habitat of the larvae was always characterized by aperiphyton community that appeared to be the primary food resource for thelarvae. These data suggest that torrential flows over appropriate substratesare important factors regulating habitat availability for T. torrenticolaand that reduced discharge (e.g. affected by water diversions) couldsignificantly reduce the amount of available habitat for this organism andother flow sensitive stream fauna.     

Impact of the infaunal Manila clam, <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>, on sediment stability

The aim of this study was to examine the impact of bioturbation by the Manila clam, Ruditapes philippinarum, on sediment stability. A laboratory benthic annular flume system (AFS) was deployed to evaluate the relationship between sediment stability of a subtidal mudflat and density of the infaunal clam under the influence of different current velocities. There was a significant correlation between mean erosion rate and current velocities in all treatments with clams (p < 0.001). There was also a significant correlation between mean erosion rate and R. philippinarum density (p < 0.001), reflecting bioturbation-enhanced sediment erosion. The effects of clam density on sediment erodability were more marked at the lower current velocities. In the control, the critical erosion velocity (Ū_crit) was about 32 cm s⁻¹. With increasing R. philippinarum density, Ū_crit decreased down to the minimum value of about 20 cm s⁻¹ at a density of 206 clams m⁻². This study demonstrated that the burrowing activity of R. philippinarum reduces sediment stability, particularly at relatively low current velocities (25 cm s⁻¹) and at densities below those found in the clam cultivation areas within the Sacca di Goro lagoon.     

Blood Viscosity and the Expression of Inflammatory and Adhesion Markers in Homozygous Sickle Cell Disease Subjects with Chronic Leg Ulcers

Objective

To determine differences in TNF-α, IL-1β, IL-10, sICAM-1 concentrations, leg hypoxia and whole blood viscosity (WBV) at shear rates of 46 sec^-1 and 230 sec^-1 in persons with homozygous S sickle cell disease (SCD) with and without chronic leg ulceration and in AA genotype controls.

Design

& Methods: fifty-five age-matched participants were recruited into the study: 31 SS subjects without leg ulcers (SS_n), 24 SS subjects with leg ulcers (SS_u) and 18 AA controls. Haematological indices were measured using an AC.Tron Coulter Counter. Quantification of inflammatory, anti-inflammatory and adhesion molecules was performed by ELISA. Measurement of whole blood viscosity was done using a Wells Brookfield cone-plate viscometer. Quantification of microvascular tissue oxygenation was done by Visible Lightguide spectrophotometry.

Results

TNF-α and whole blood viscosity at 46 sec^-1 and 230 sec^-1 (1.75, 2.02 vs. 0.83, 1.26, p<0.05) were significantly greater in sickle cell disease subjects than in controls. There were no differences in plasma concentration of sICAM-1, IL-1β and IL-10 between SCD subjects and controls. IL-1β (median, IQR: 0.96, 1.7 vs. 0, 0.87; p<0.01) and sICAM-1 (226.5, 156.48 vs. 107.63, 121.5, p<0.005) were significantly greater in SS_u group compared with SS_n. However there were no differences in TNF-α (2, 3.98 vs. 0, 2.66) and IL-10 (13.34, 5.95 vs. 11.92, 2.99) concentrations between SS_u and SS_n. WBV in the SS_u group at 46 sec^-1 and at 230 Sec 1 were 1.9 (95%CI; 1.2, 3.1) and 2.3 (1.2, 4.4) times greater than in the SS_n group. There were no differences in the degree of tissue hypoxia as determined by lightguide spectrophotometry.

Conclusion

Inflammatory, adhesion markers and WBV may be associated with leg ulceration in sickle cell disease by way of inflammation-mediated vasoocclusion/vasoconstriction. Impaired skin oxygenation does not appear to be associated with chronic ulcers in these subjects with sickle cell disease.     

Symmetrical and asymmetrical gaits in the mouse: patterns to increase velocity

The gaits of the adult SWISS mice during treadmill locomotion at velocities ranging from 15 to 85 cm s^–1 have been analysed using a high-speed video camera combined with cinefluoroscopic equipment. The sequences of locomotion were analysed to determine the various space and time parameters of limb kinematics. We found that velocity adjustments are accounted for differently by the stride frequency and the stride length if the animal showed a symmetrical or an asymmetrical gait. In symmetrical gaits, the increase of velocity is provided by an equal increase in the stride length and the stride frequency. In asymmetrical gaits, the increase in velocity is mainly assured by an increase in the stride frequency in velocities ranging from 15 to 29 cm s^–1. Above 68 cm s^–1, velocity increase is achieved by stride length increase. In velocities ranging from 29 to 68 cm s^–1, the contribution of both variables is equal as in symmetrical gaits. Both stance time and swing time shortening contributed to the increase of the stride frequency in both gaits, though with a major contribution from stance time decrease. The pattern of locomotion obtained in a normal mouse should be used as a template for studying locomotor control deficits after lesions or in different mutations affecting the nervous system.     

Compartment analysis of plant cells by means of turgor pressure relaxation: II. Experimental results onChara corallina

Summary The three-compartment model (paper I) described turgor pressure relaxations as a sum of two exponential functions. The predicted shape of the curves could be confirmed inChara corallina by improving the recording and processing of data. An evaluation on the basis of the three-compartment model provided values for the hydraulic conductivity of the plasmalemma ofLp _p=2×10^–5 to 4×10^–5 cm sec^–1 bar^–1 and ofLp _i=3×10^–5 to 1×10^–4 cm sec^–1 bar^–1 for the tonoplast (assuming the area to be 90% of the plasmalemma area). The mean proportion of the total volume occupied by the cytoplasm was calculated to be 9%. This value is consistent with the concept of a highly vacuolated cell. Other explanations for the biphasic relaxation curves are discussed.