Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

Feeding rate inhibition in crowded Daphnia pulex

Feeding rates of Daphnia pulex fed a range of levels of the alga Chlamydomonas reinhardi of 15 °C are strongly density-dependent. At lower densities, Daphnia (30 1^–1) fed at higher rates than crowded (270 1^–1) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 – 15.7 × 10⁴ cells d^–1h^–1 (on a volume basis, 12.1 – 22.2 × 10⁶ m³), at 270 L^–1 3.7 – 3.9 × 10⁴ (5.2 – 5.5 = 10⁶ m³ cells d^–1h^–1 when feeding on algae at 80 000 cells ml^–1 (11.3 × 10⁶ m³ ml^–1). The feeding rate data best fit an Ivlev feeding function. An autoallelopath might be causing the repression. Water preconditioned with crowded Daphnia completely repressed feeding in uncrowded Daphnia after six hours.     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Seasonal dynamics of metabolic activity of the Daphnia community in Lake Bled (Slovenia)

Seasonal changes of the community composition, oxygen consumption (R) and respiratory electron transport system (ETS)-activity of the Daphnia community living in Lake Bled (Slovenia) were studied between January and December 1998. The ETS activity of ovigerous Daphnia females at in situ temperature ranged from 3.27 l O₂ mg dw^–1 h^–1 in February to 20.91 l O₂ mg dw^–1 h^–1 in July. Respiration rates at in situ temperature varied from 4.04 l O₂ mg dw^–1h^–1 in December to 18.68 l O₂ mg dw^–1 h^–1in July. The influence of four factors (temperature, body size, fecundity, genetic differences) on the metabolism were investigated. Both ETS activity and respiration rate significantly correlated with temperature. The proportion of hybrid D. cucullata× galeata in Daphnia community correlated significantly with respiration rate at in situtemperature and ETS activity at standard temperature also. ETS activity and respiration rate showed no significant correlation with body size and the fecundity of Daphnia, whereas ETS activity in D. hyalina × galeata and D. cucullata× galeataseparately correlated with body size. ETS activity of D. hyalina × galeata also was correlated with fecundity. Hybrid D. hyalina× galeata had up to one third lower ETS activity than D. cucullata× galeata. The mean ETS/R ratio in the Daphnia community was 1.16±0.28 (N= 12). The ETS/R ratio did not correlate significantly with temperature, body size, fecundity or the proportion of D. cucullata× galeatain the Daphnia community. Laboratory experiments showed that both hybrids had similar ETS/R ratios.     

Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.     

Light response of D1 turnover and photosystem II efficiency in the seagrassZostera capricorni

Biochemical and biophysical parameters, including D1-protein turnover, chlorophyll fluorescence, oxygen evolution activity and zeaxanthin formation were measured in the marine seagrassZostera capricorni (Aschers) in response to limiting (100 mol·m^–2·^–1), saturating (350 mol·m^–2·s^–1) or photoinhibitory (1100 mol·m^–2·s^–1) irradiances. Synthesis of D1 was maximal at 350 mol·m^–2·s^–1 which was also the irradiance at which the rate of photosynthetic O₂ evolution was maximal. Degradation of D1 was saturated at 350 mol·m^–2·s^–1. The rate of D1 synthesis at 1100 mol·m^–2·s^–1 was very similar to that at 350 mol·m^–2·s^–1 for the first 90 min but then declined. At limiting or saturating irradiance little change was observed in the ratio of variable to maximal fluorescence (Fv/Fm) measured after dark adaptation of the leaves, while significant photoinhibition occurred at 1100 mol·m^–2·s^–1. The proportion of zeaxanthin in the total xanthophyll pool increased with increasing irradiance, indicative of the presence of a photoprotective xanthophyll cycle in this seagrass. These results are consistent with a high level of regulatory D1 turnover inZostera under non-photoinhibitory irradiance conditions, as has been found previously for terrestrial plants.We would like to thank Professor Peter Böger (Department of Plant Biochemistry, University of Konstanz, Germany) for the kind gift of D1 antibodies. This work was partly supported by a University of Queensland Enabling Grant to CC.     

The phytoplankton of Lake Liddell,New South Wales: chlorophyll a concentrations,species seasonal succession,and covariation with nutrients

Samples of the phytoplankton in a freshwater lake, Lake Liddell, New South Wales (Lat: 32° 22 S, Long. 150° 1 E) were collected every 4 weeks between October 1987 and November 1988. Chlorophyll a concentrations ranged from 1.8 g 1^–1 to 9.1 g 1^–1 and were positively correlated with the following nutrient parameters: total and nett mass additions of nitrate/nitrite-N and total-N, total additions of Kjeldahl-N, and nett mass addition N-P ratios. There was no correlation between lake nutrient concentrations and chlorophyll a. Factors other than nutrient concentrations appeared to be effecting chlorophyll a concentrations as summer levels were low despite nutrient concentrations being at a maximum. In spring and summer the phytoplankton was dominated by chlorophytes, with dinoflagellates and diatoms most abundant in autumn. During winter cyanobacteria were the most abundant. The relative abundance of chlorophytes was positively correlated with in lake nitrate/nitrite-N concentrations whereas the relative abundance of cyanobacteria was negatively correlated with this parameter. Based on chlorophyll a concentrations and the phytoplankton flora Lake Liddell can be classified as mesotrophic.     

The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l^–1 d^–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l^–1 d^–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l^–1 d^–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l^–1 d^-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l^–1 d^–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l^–1 d^–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.     

Long-term phytoplankton changes in an artificially divided,top-down manipulated humic lake

Lake Große Fuchskuhle (Brandenburg, Germany) is a naturally acidic bog lake that was artificially divided into four basins by large plastic curtains for biomanipulation experiments in 1990. Different numbers of perch were added to each compartment beginning in the spring of 1993. The species composition and abundance of phytoplankton, pH, nutrient concentrations, dissolved organic carbon (DOC) and chlorophyll a content were analyzed at regular intervals during 1991 and 1998. The division of the lake resulted in divergent developments in the physical and chemical environment of the compartments. This study compared the phytoplankton assemblages of the Northeast- (NE) and Southwest- (SW) basins which differed strongly in chemistry during the investigation period. Divergent developments in phytoplankton species composition in both basins can be explained by changes in physical and chemical conditions (bottom-up effects). Increased pH values and DOC concentrations probably favoured mass developments of the dinoflagellate Gymnodinium uberrimum since 1993, while increased nutrients (dissolved inorganic carbon, total nitrogen and especially total phosphorus) as well as further changes in pH and DOC led to the dominance of the raphidophyte Gonyostomum semen in 1998. This bloom was characterized by extreme biomasses of up to 143 mg l^–1 wet weight, corresponding with high chlorophyll a concentrations of up to 413 g l^–1 at the same time. In contrast, no significant relationship between experimental manipulations by piscivorous fish stocking (top-down effects) and phytoplankton biomass were observed.     

Screening yeast cells for absorption of selenium oxyanions

Certain yeast cells on solid nutrient medium produced colonies surrounded by a light zone of selenite absorption. This screening procedure resulted in the selection of 22 strains out of 200 isolates with different Se⁴⁺-absorbing capacity ranging from 16 to 98.8 g Se⁴⁺ g^–1 l^–1 h^–1. The highest rate of Se⁴⁺ elimination from the Na₂SeO₃ solution was observed with an oval shaped, cream pigmented fermentative yeast, tentatively called Candida sp. strain MS4. This strain was isolated from wastewater and found to accumulate selenium oxyanions. Se⁴⁺ uptake involved both inactive and active phenomena. The amounts of selenium (initial concentration 2 mg Se⁴⁺ l^–1) removed from aqueous solution by inactive and active phenomena were 667 g Se⁴⁺ g^–1 l^–1, and 1580 g Se⁴⁺ g^–1 l^–1, respectively. The strain also removed selenate inactively (135 g Se⁶⁺ g^–1 l^–1).     

Influence of environmental factors on the growth in culture of a New Zealand strain of the fast-spreading algaHydrodictyon reticulatum (water-net)

Hydrodictyon reticulatum (L.) Lagerh. is a recent addition to the New Zealand flora and is expanding its distribution rapidly. Proliferations of the alga now constitute an economic nuisance in waters which have not previously suffered filamentous algal blooms. To better understand the current and likely future spread of the alga and to identify possible management options the alga's growth requirements have been investigated. A strain isolated from New Zealand tolerated temperatures between 5 and 40 °C and salinities from 0 to 5. Optimal growth was at 25 °C, 150 mol photon m^–2s^–1 and in freshwater. Nett photosynthesis was saturated at photon flux densities of 100 and 160 mol m^–2s^–1 at 12 and 20 °C, respectively. Growth rate was linearly related to internal N concentration and hyperbolically to internal P concentration. Minimum cellular nutrient contents, by weight, were 1% N and 0.2% P. Growth was saturated at contents of 5% N and 0.5% P under the conditions of culture (20 °C, 150 mol photon m^–2s^–1). The alga maintained optimal cellular N content at low ambient nitrate concentrations (100 mg m^–3) half optimum content at 18 mg m^–3. Affinity for filtrable reactive phosphorus was not unusually high compared to other filamentous algae. We suggest that this alga is occupying a niche in New Zealand which has been precluded from other filamentous nuisance algae by low N concentration and N:P ratio. The significance of these findings in setting environmental targets for management of this nuisance alga is discussed.Author for correspondence     

Grazing by a dominant rotifer Conochilus unicornis Rousselet in a mountain lake: in situ measurements with synthetic microspheres

Grazing rates of zooplankton were analysed in the summer of 1999 in Yellow Belly Lake, an oligotrophic system in the Sawtooth Mountains of Idaho (U.S.A.). The colonial rotifer Conochilus unicornis was a dominant species in the epilimnion, with densities reaching 20 colonies l^–1 (ca. 400 ind. l^–1). Clearance rates were measured with an in situ Haney Grazing chamber and synthetic microspheres 5, 9 and 23m in diameter. At epilimnetic temperatures of around 14 °C, mean clearance rates for 5m particles ranged from 30 to 65 l ind.^–1 h ^–1. Clearance rates were 2–9 times higher on the 5m spheres than on the 9 m spheres, and C. unicornis almost never fed on the 23 m spheres. Grazing rates did not change over the diel cycle. Clearance rates declined more than 10-fold as temperatures declined from 14 °C in the epilimnion to 7 °C in the metalimnion. In the epilimnion, grazing by C. unicornis was more important than grazing by crustaceans in the community, at least on particles 9m. The results show the importance of grazing by rotifers in lakes, and the significance of spatial variations that influence grazing rates.     

N2 fixation by red alder (Alnus rubra) and scotch broom (Cytisus scoparius) planted under precommerically thinned Douglas-fir (Pseudotsuga menziesii)

Summary From acetylene reduction assays over a 10-month period starting in April 1979, nodule activities averaged 18.78 (se 4.67) moles C₂H₄ g nodule dw^–1 h^–1 forAlnus rubra and 59.95 (se 12.14) moles C₂H₄ g nodule dw^–1 h^–1 forCytisus scorparius. Plant rates were 1.91 (se. 47) moles C₂H₄ plant^–1 h^–1 forA. rubra and 0.55 (se. 17) moles C₂H₄ plant^–1 h^–1 forC. Scoparius. Plant activity and total leaf N were strongly correlated with the dw of other plant parts, but nodule activity and percent leaf N were not. Plant and nodule activities were not associated with temperature, moisture stress, precipitation events or percent light for either species over the growing season nor for 54A. rubra sampled in mid-season 1979 on one replication. After 5 to 6 growing seasons, 14A. rubra on the same site ranged from 30 to 332 cm in height and showed strong correlation between nodule dw, leaf dw, plant size and total leaf N. Results from this study and others indicate logistic equations may be modified to predict the effect of adding a N₂ fixing plant to a population of non N₂ fixing trees.     

Utilisation of soil organic P by agroforestry and crop species in the field,western Kenya

A field experiment in western Kenya assessed whether the agroforestry species Tithonia diversifolia (Hemsley) A. Gray, Tephrosia vogelii Hook f., Crotalaria grahamiana Wight & Arn. and Sesbania sesban (L) Merill. had access to forms of soil P unavailable to maize, and the consequences of this for sustainable management of biomass transfer. The species were grown in rows at high planting density to ensure the soil under rows was thoroughly permeated by roots. Soil samples taken from beneath rows were compared to controls, which included a bulk soil monolith enclosed by iron sheets within the tithonia plot, continuous maize, and bare fallow plots. Three separate plant biomass samples and soil samples were taken at 6-month intervals, over a period of 18 months. The agroforestry species produced mainly leaf biomass in the first 6 months but stem growth dominated thereafter. Consequently, litterfall was greatest early in the experiment (0–6 months) and declined with continued growth. Soil pH increased by up to 1 unit (from pH 4.85) and available P increased by up to 38% (1 g P g^–1) in agroforestry plots where biomass was conserved on the field. In contrast, in plots where biomass was removed, P availability decreased by up to 15%. Coincident with the declines in litterfall, pH decreased by up to 0.26 pH units, plant available P decreased by between 0.27 and 0.72 g g^–1 and P_o concentration decreased by between 8 and 35 g g^–1 in the agroforestry plots. Declines in P_o were related to phosphatase activity (R²=0.65, P<0.05), which was greater under agroforestry species (0.40–0.50 nmol MUB s^–1 g^–1) than maize (0.28 nmol MUB s^–1 g^–1) or the bare fallow (0.25 nmol MUB s^–1 g^–1). Management of tithonia for biomass transfer, decreased available soil P by 0.70 g g^–1 and P_o by 22.82 g g^–1. In this study, tithonia acquired P_o that was unavailable to maize. However, it is apparent that continuous cutting and removal of biomass would lead to rapid depletion of P stored in organic forms.     

Filtering impacts of larval and sessile zebra mussels (Dreissena polymorpha) in western Lake Erie

Summary We assessed the feeding biology of veliger larvae of the introduced zebra mussel (Dreissena polymorpha Pallas) in laboratory experiments using inert microspheres as food analogues. Mean clearance rate on 2.87-m beads ranged between 247 and 420 L veliger^–1 day^–1. Clearance rate was unrelated to bead concentration up to 100 beads L^–1, but was positively correlated with veliger shell length. Clearance rates of Dreissena veligers are within the range of those reported for marine bivalve veligers of similar size and for herbivorous Great Lakes microzooplankton, but are orders of magnitude lower than those of settled, conspecific adults. The impact of settled zebra mussel grazing activities on phytoplankton stocks may be up to 1162 times greater than that exerted by veliger populations in western Lake Erie. Based on 1990 size-frequency distributions and associated literature-derived clearance rates, reef-associated Dreissena populations in western Lake Erie (mean depth 7 m) possess a tremendous potential to filter the water column (up to 132 m³ m^–2 day^–1) and redirect energy from pelagic to benthic foodwebs. Preliminary analyses indicate that chlorophyll a concentration is strongly depleted (<1 g L^–1) above Dreissena beds in western Lake Erie.     

Increased taxane accumulation in callus cultures of Taxus cuspidata and Taxus × media by some elicitors and precursors

In Taxus cuspidata callus, vanadyl sulfate (10 mg l^–1) induced a high (146 g g^–1 dry wt) production of 10-deacetylbaccatin III in comparison to 7 g g^–1 dry wt of the control. The content of paclitaxel in this species increased from 16 g g^–1 to 74 g g^–1 dry wt when 20 mg phenylalanine l^–1 was used. In T. media, p-aminobenzoic acid induced the highest content of 10-deacetylbaccatin III (481 g g^–1 dry wt) versus 181 g g^–1 in the control. Paclitaxel increased from 89 to 139 g g^–1 dry wt after adding chitosan (20 mg l^–1) to the cultures.     

Phytoextraction of selenium from soils irrigated with selenium-laden effluent

This two-part study compared the efficacy of different plant species to extract Se from soils irrigated with Se-laden effluent. The species used were: Brassica napus L. (canola), Brassica juncea Czern L. and Coss (Indian mustard), and Hordeum vulgare L. (barley). In Study 1 we irrigated the plants with a saline effluent containing 0.150 mg Se L^–1, while in Study 2, the same species were planted in a saline soil selenized with 2 mg Se L^–1. Plants were simultaneously harvested 120 days after planting. In Study 1, there were only slight effects of treatment on dry matter (DM) yield. Plant Se concentrations averaged 21 g Se g^–1DM for the Brassica species, and 4.0 g Se g^–1 DM for barley. Total Se added to soils via effluent decreased by 40% for Brassica species and by 20% for barley. In Study 2, total DM decreased for all species grown in saline soils containing Se. Plant Se concentrations averaged 75 g g^–1 DM for Brassica species and 12 g Se g^–1 DM for barley. Total Se added to soils prior to planting decreased by 40% for Brassica species and up to 12% for barley. In both studies, plant accumulation of Se accounted for at least 50% of the Se removed in soils planted to Brassica and up to 20% in soils planted to barley. Results show that although the tested Brassica species led to a significant reduction in Se added to soil via use of Se-laden effluent, additional plantings are necessary to further decrease Se content in the soil.     

Photolithotrophy,photoheterotrophy and chemoheterotrophy during spring phytoplankton development (Lake Pavin)

In order to determine the relative importance of autotrophic and heterotrophic activities in both bacterial and phytoplanktonic communities in an oligomesotrophic lake, the size fractionation by differential filtration and the use of a bacterial inhibitor (gentamycin) were combined. The study was carried out at Lake Pavin during the spring planktonic bloom. Photosynthetic and photo- and chemoheterotrophic activities were measured from the assimilation of NaH¹⁴CO₃ and glucose-³H, using a double labeling technique. The bacterial community was at low cell concentration (0.6 to 7 × 10⁵ cells ml^–) and represented very low biomass values (0.9 to 11.5 gC liter^–1). The abundance of the phytoplankton varied between 0.5 and 1.8 × 10⁶ cells liter^–1, and biomass values ranged between 19 and 118 gC liter^–1. The diatom Melosira italica sp. subarctica (O. Mueller) was the largely dominant species in the meta- and hypolimnion. Inorganic fixation by photolithotrophy (mean value: 1.66 mg C m^–3 hour^–1) largely predominates over assimilation by photoheterotrophy (mean value: 0.93 g C m^–3 hour^–1) or chemoheterotrophy (mean value: 2.42 g C m^–3 hour^–1). However, because of the considerable underestimation of heterotrophic assimilation due to the experimental methods used, and because of the spatial and temporal separation of photolithotrophic and photo- and chemoheterotrophic activities, it is likely that the fixation of organic carbon by microalgae plays an important role in the survival of species and/or in competitive interactions, as the results with Monoraphidium contortum (Pasch. et Korschik.), the prevailing species in the epilimnion, would suggest. Send offprint requests to: C. Amblard.     

Phenylacetic acid-induced somatic embryogenesis in cultured hypocotyl explants of geranium (Pelargonium x hortorum Bailey)

Summary The effect of a non-indole compound, phenylacetic acid (PAA), on the induction of somatic embryogenesis in tissue cultures of geranium (Pelargonium x hortorum Bailey cv. Scarlet Orbit Improved) was investigated. Hypocotyl explants derived from young, dark-grown seedlings were cultured on Murashige and Skoog (1962) medium (MS) supplemented with PAA or IAA (0.01–120 M) alone or in combination with BAP (8 M). Somatic embryogenesis was induced by both PAA and IAA at 0.01–20 M with 8 M BAP, however, the optima differed considerably for the two compounds. Maximal activity of IAA for somatic embryogenesis was found at 0.1–2.5 M, whereas PAA gave best results at 10 and 20 M under identical culture conditions. Higher concentrations (30–120 M) of IAA or PAA in the medium induced callusing in the explants, but the callus was neither embryogenic nor morphogenic.Abbreviations BAP N⁶-benzylaminopurine - IAA indole-3-acetic acid - MS Murashige and Skoog (1962) - PAA phenylacetic acid