THE COMPARATIVE CELL CYCLE AND METABOLIC EFFECTS OF CHEMICAL TREATMENTS ON ROOT TIP MERISTEMS. I. IOXYNIL

In this study we investigated the cell cycle response of Vicia faba and Pisum sativum root tip meristems to ioxynil treatments at two concentrations, (10^−-4m and 10^−-6m ). After 24 h of treatment at 10^−-4m concentration, O₂ uptake and ATP concentrations were significantly reduced. The mitotic index was reduced and the cell cycle population position was shifted to indicate that previously inhibited cells reformed their nuclei and became tetraploid. Prolonged treatment at this concentration resulted in cell death. Treatment with ioxynil at 10^−-6m reduced the rate of entry into mitosis. Abnormal mitotic figures in all stages were observed, and the ploidy level of mitotically inhibited cells was doubled. These observations indicated that at 10^−-6m concentration ioxynil acts as a preprophase inhibitor, that is, it does not act directly on the mitotic apparatus but does affect processes on which mitosis depends.     

EFFECT OF HORMONES AND VITAMIN B12 ON GAMETOPHORE DEVELOPMENT IN THE MOSS PYLAISIELLA SELWYNII

Bud formation in the moss Pylaisiella selwynii is greatly enhanced by cytokinins at concentrations as low as 10⁻¹²m , yet these buds usually fail to develop into normal gametophores. Various ratios at different concentrations of the cytokinin N-6-γ,γ-dimethylallylaminopurine to indoleacetic acid failed to enhance bud initiation over that obtained with cytokinin alone or to permit normal gametophore development. Deletion of the cobaltous ions from the culture medium prevented the appearance of the few gametophores usually formed in the complete medium, but different amounts of cobaltous ion did not significantly enhance initiation of gametophore development. Bud initiation was enhanced 3- to 20-fold by vitamin B₁₂ at 10⁻⁵m or by B₁₂ coenzyme at 10⁻⁴m , and the time of appearance of these buds was advanced by 6–12 days compared to control plants. At these concentrations of the B₁₂ compounds the buds formed normal gametophores, but at 10⁻⁴m vitamin B₁₂ they grew into callus-like masses similar to those obtained with cytokinins. Although the effects of B₁₂ on bud initiation and development mimicked those of cytokinins, except in permitting normal development, no additive or synergistic effects were observed when they were tested together. It is suggested that B₁₂ may play a regulatory role in the control of gametophore initiation and development in mosses.     

PROPERTIES OF TYROSINE HYDROXYLASE IN PERIPHERAL NERVES

Approximately 80 per cent of tyrosine hydroxylase activity in bovine mandibular nerve and rabbit sciatic nerve was soluble, and the rest of the activity was particle-bound. The soluble enzyme in bovine mandibular nerve was isolated by ammonium sulphate fractionation (25–35 per cent saturation). The enzyme had a pH optimum at 5·9 in Tris-acetate buffer, and at 6·5 in Tris-HCl or phosphate buffer. The enzyme required a tetrahydropteridine cofactor. K_m values toward various tetrahydropteridines such as l -erythro-tetrahydrobiopterin (a probable natural cofactor), 2-amino-4-hydroxy-6-methyltetrahydropteridine, and 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine were 2 × 10⁻⁵m , 5 × 10⁻⁵m and 4 × 10⁻⁴m , respectively. The K_m value for tyrosine at 1 × 10⁻³m -2-amino-4-hydroxy-6-methyltetrahydropteridine as a cofactor was 5 × 10⁻⁵m . The enzyme activity was markedly stimulated with Fe²⁺ or catalase, but Fe²⁺ gave higher activity. The activity was inhibited with α, α′-dipyridyl, l -α-methyl-p-tyrosine, and various catecholamines. Among catecholamines, dopamine was the most potent inhibitor. l -5-Hydroxytryptophan was an inhibitor as potent as dopamine. Neither d -5-hydroxytryptophan nor 5-hydroxytryptamine inhibited the enzyme. The inhibition by l -5-hydroxytryptophan was partially competitive with tetrahydrobiopterin at concentrations higher than 9 × 10⁻⁵m , and partially uncompetitive at concentrations lower than 9 × 10⁻⁵m . The addition of heparin or lysolecithin did not affect enzyme activity with tetrahydrobiopterin as cofactor.     

INFLUENCE OF CERTAIN PLANT GROWTH REGULATORS AND CROWN-GALL RELATED SUBSTANCES ON BUD FORMATION AND GAMETOPHORE DEVELOPMENT OF THE MOSS PYLAISIELLA SELWYNII

Bud formation and gametophore development were studied in the moss Pylaisiella selwynii (Kindb.) Steere and Anderson grown from spores in a liquid medium consisting of inorganic salts. Indoleacetic acid and ethrel increased bud formation within a narrow concentration range. Copious bud formation was obtained with the five cytokinins tested at concentrations varying from 5 X 10⁻⁶ to 5 X 10⁻¹⁴ M. Except for about 10 % of the buds obtained with 6-γ, γ-dimethylallylaminopurine at 5 times 10⁻¹⁴ m, the cytokinin-induced buds failed to develop into normal gametophores. Octopine, lysopine, and octopinic acid, substances obtained from crown-gall tumors, increased bud formation at 10⁻³ m. On lysopine-treated plants these buds developed into typical gametophores. Gemma-like structures were obtained with octopine but no gametophores. l -arginine and l -lysine, the amino acids which respectively occur in octopine and lysopine, failed to induce gametophore formation although buds were obtained with 10⁻³ m lysine. γ-Guanidinobutyric acid induced bud formation at 10⁻³ m, but these buds developed into highly abnormal gametophores. The failure of buds obtained with many of these treatments to develop into gametophores appeared to result from the formation of new cell walls in other than the normal geometrical relationship during initial divisions of the pro-bud. The relevance of the findings to the crown-gall problem is discussed.     

Effects of Analogs of the Fungal Sexual Pheromone Sirenin on Male Gamete Motility in Allomyces macrogynus

The ability of various structural analogs of the sexual pheromone sirenin to attract male gametes of the aquatic fungus Allomyces macrogynus was determined. Previous studies had shown that several structural analogs and stereoisomers of natural l-sirenin were devoid of activity at physiological concentrations. We now report the discovery of a structural analog that exhibits biological activity indistinguishable from the natural pheromone. The bioassay system used to determine chemotaxis was calibrated using synthetic, racemic sirenin, which exhibited a threshold concentration for gamete attraction at an applied concentration of 10 picomolar. The new synthetic monohydroxy analog of sirenin also had a threshold concentration of 10 picomolar. In the process of developing a new total synthesis of sirenin, a variety of other analogs were prepared and tested. All of these analogs exhibited threshold concentrations at 1 micromolar or higher, although attraction at these higher concentrations still varied according to their structural resemblance to sirenin. Thus, the results of these studies demonstrate that the hydroxymethyl group attached to the six-membered ring of sirenin is not essential for biological activity at physiological concentrations. The studies with other analogs demonstrate that biological activity at any concentration involves a balance between hydrophilic hydroxyl groups and hydrophobic hydrocarbon groups in the structure.     

FACTORS AFFECTING THE TOXICITY OF SEVERAL LICHEN ACIDS: EFFECT OF PH AND LICHEN ACID CONCENTRATION

The effect of pH 5–8 and lichen acid concentration gradients (2.7 times 10⁻² - 2.7 times 10⁻⁶ m ) on the toxicity of the following lichen acids: usnic, lecanoric, evernic, vulpinic, stictic, fumarpro-tocetraric, psoromic, and atranorin, on spores of Funaria hygrometrica was tested. Percent germination and sporeling growth were used as indicators of toxicity. None of the lichen acids were significantly toxic, for either percent germination or sporeling growth at concentrations equal to or below 2.7 times 10⁻⁵ m at pH 7.0, but many of the lichen acids which increased in toxicity at values different from pH 7 may have been toxic at lower concentrations if a different pH was used for the assay. Lichen acid toxicity showed a good correlation with pH for the parameter of spore germination, or sporeling growth, or both. Some lichen acids did not inhibit germination but were effective in retarding sporeling growth, or vice versa. This observation is discussed in relation to changing fatty acids and other lipid composition as germination occurs. Two of the three O-methylated lichen acids (evernic and psoromic) were among the most effective in inhibiting growth over all, but at lower pH values these were less effective than non-O-methylated lichen acids. Stictic, which is also an O-methylated lichen acid, was the least effective inhibitor over all the pH values for both parameters, while vulpinic was the most toxic over all the pH values. The order of relative toxicity for the lichen acids is different, depending on the pH and concentration at which they are tested and depending on the parameter measured. Thus, in an ecological sense, it is difficult to evaluate the adaptive significance of a particular compound or group of compounds without knowing what factors influence the toxicity of those compounds and how these factors vary in the organism's habitat.     

APICAL DOMINANCE: THE EFFECTS OF GROWTH REGULATORS ON THE GAMETOPHYTE OF ANEMIA PHYLLITIDIS

Gametophytes of the fern, Anemia phyllitidis (L.) Sw. were aseptically cultured until nearly mature, then collected and surgically divided into meristematic and nonmeristematic halves. Indoleacetic acid, benzyladenine, abscisic acid, and the auxin inhibitor, triiodobenzoic acid, were employed to elucidate the role of growth regulators during regeneration of adventitious gametophytes. Explants possessing actively growing meristems failed to produce adventitious thalli regardless of treatment. Untreated nonmeristematic halves initiated numerous filamentous outgrowths within two weeks of excision. These outgrowths eventually developed into the cordate prothalli typical of this species. Nontoxic levels of IAA (10⁻⁴ g/1 and 10⁻⁵ g/1) promoted early regeneration by basal explants. TIBA, at 10⁻⁵ m, completely suppressed regeneration. Benzyladenine, at 10⁻² g/1, exerted its most striking effect by greatly increasing the number of adventitious outgrowths formed by treated basal explants. ABA at all concentrations delayed regeneration and reduced the number of basal halves that displayed renewed mitotic activity. This evidence suggests that auxin acts as an essential promoter of regeneration, and that the maintenance of endogenous hormonal interactions is necessary to preserve the form of an intact gametophyte.     

EFFECTS OF AUXIN ON CELL ENLARGEMENT IN FERN GAMETOPHYTES: DEVELOPMENTAL STAGE OF THE CELL AND RESPONSE TO AUXIN

When gametophytes of Onoclea sensibilis are placed on an auxin-containing medium in darkness, the cells of the plant increase in length and width. Measurements were made to determine the effects of cell age and auxin concentration on the magnitude of the cells’ response. When comparing final size with size before auxin treatment, the youngest cells have the greatest response. However, they also have the greatest endogenous growth. The optimum auxin concentration for increase in length changes with the age of the cells. The greatest length is attained in young cells with an auxin concentration of 10^−-6–10^−-7 m; 10^−-5 m auxin is supraoptimal. The greatest increase in width of the cells is produced by 10^−-5 m auxin, regardless of cell age. The data are believed best to be interpreted as showing an age-dependent change in the capacity of the cells to respond to auxin.     

THE CONVULSANT ACTION OF METHYLDITHIOCARBAZINATE: A COMPARISON WITH OTHER SULPHUR-CONTAINING HYDRAZIDES

—The convulsant action of methyldithiocarbazinate (MDTC), thiocarbohydrazide (TCH) and thiosemicarbazide (TSC) has been studied in mice. The relationship between dose and time to convulsions indicated that MDTC has a dual action and is more potent than TSC. Pretreatment of mice with pyridoxal phosphate (0.25 mmol/kg) protected against convulsions and death produced by low doses of MDTC or TCH, and low or high doses of TSC. Pretreatment with pyridoxine hydrochloride (0.25 mmol/kg) protected mice against TSC but not against TCH. It protected against low doses of MDTC (0.12 mmol/kg), but shortened the latency to convulsions after intermediate doses of MDTC (0.37 mmol/kg). Glutamate decarboxylase activity (GAD, EC 4.1.1.15) in whole brain homogenates from mice killed at the onset of seizures, was significantly reduced by all 3 drugs at all doses. This inhibition did not exceed 30% after any dose of TSC or TCH, but was 64% in mice killed 4 min after the injection of MDTC (0.98 mmol/kg). The addition of pyridoxal phosphate to brain homogenates abolished GAD inhibition after MDTC but not after TCH. In vitro brain GAD was 50% inhibited by 10⁻⁴m -MDTC, 18% by 10⁻⁴m -TSC and 8% by 10 ⁻⁴m -TCH. Kinetic studies suggested that at low concentrations MDTC inhibits by competing with pyridoxal phosphate. At the onset of convulsions the cerebral content of pyridoxal phosphate was reduced after low or high doses of TSC (0.27 and 2.2 mmol/kg) and after high doses of MDTC (0.98 mmol/kg). All three drugs (at 10⁻⁵−10⁻⁴m ) inhibited pyridoxal phosphokinase (EC 2.7.1.35) in vitro. Short latency convulsions after MDTC (0.37–0.98 mmol/kg) very probably arise from inhibition of cerebral GAD, due to competition for coenzymic sites and/or unavailability of coenzyme. Long-latency convulsions after MDTC (0.12–0.37 mmol/kg) are comparable to those seen after TSC (0.27–2.2 mmol/kg) and may depend on a mechanism additional to inhibition of GAD.     

THE EFFECT OF AUXIN AND GUANINE ON CELL EXPANSION AND CELL DIVISION IN THE GAMETOPHYTE OF THE FERN,ONOCLEA SENSIBILIS

Miller , J. H. (Yale U., New Haven, Conn.) The effect of auxin and guanine on cell expansion and cell division in the gametophyte of the fern, Onoclea sensibilis. Amer. Jour. Bot. 48(9): 816–819. Illus. 1961.—Auxin and guanine promote cell expansion in 0. sensibilis gametophytes. The optimum concentration of auxin for total expansion is 10^−-5 M, but the optimum for elongation is 10^−-6 M. Above this concentration the cells expanded isodiametrically. Guanine is active at higher concentrations than auxin. Increasing concentrations of auxin progressively inhibit red light-induced cell division, while guanine has no effect on cell division. Neither kinetin nor adenine promotes cell expansion or cell division.     

BIOLOGICAL AND CHEMICAL CHARACTERISTICS OF THE GIANT DIATOM ETHMODISCUS (BACILLARIOPHYCEAE) IN THE CENTRAL NORTH PACIFIC GYRE

Cells of the giant diatom Ethmodiscus Castr. gathered from the upper 15 m were examined for O₂ evolution, nitrate reductase activity (NRA), C and N composition, internal NO concentrations, , and ¹⁵NO, ¹⁵NH , and ³²Si uptake in a series of cruises in the central N. Pacific gyre. The δ¹⁵N (2.56–5.09 ‰), internal NO concentrations (0.0– 11.5 mM NO⁻), and NRA (6.7 ± 4.7 × 10⁻⁴μM NO cell ⁻¹·h⁻¹) were consistent with recent exposure to elevated nitrate concentrations and utilization of deep NO as a primary N source. These results are similar to other diatoms that migrate vertically to the nutricline as part of their life cycle. Rate measures (Si[OH]₄ uptake, NRA, and O₂ evolution) indicated surface doubling times from 45 h to 75 h. Both NO and NH uptake in surface waters were low and inadequate to supply N needs at surface NO and NH concentrations. Our results suggest a partitioning in nutrient acquisition, with N acquired at depth and C and Si acquired at the surface. Doubling rates were two to three times higher than predicted from cell volume and C content models. These data are consistent with the observed elemental content being lower than expected because of the dominance of cell volume by the vacuole. Our calculations suggest that Ethmodiscus contributes little to the biogeochemistry of the upper water column via upward nutrient transport. Although reported as a paleo-upwelling indicator, thisevidence suggests that Ethmodiscus has adapted to the nutrient-poor open ocean by a vertical migration strategy and has biological characteristics inconsistent with a upwelling indicator.     

SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂SeO₃ to nutrient enriched artificial seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10⁻² M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga find all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

REGULATION OF GROWTH AND CELLULAR DIFFERENTIATION IN DEVELOPING AVENA INTERNODES BY GIBBERELLIC ACID AND INDOLE-3-ACETIC ACID

Auxin (IAA) at physiological concentrations causes significant reduction of GA₃-promoted growth in excised Avena stem segments. IAA is thus considered to be a gibberellin antagonist in this system. It was found to act non-competitively in repressing GA₃-augmented growth in these segments. In intercalary meristem cells at the base of the elongating internode, GA₃ blocks cell division activity and causes a marked increase in cell lengthening. IAA substantially promotes lateral expansion in comparable intercalary meristem cells, particularly in the vicinity of vascular bundles underlying the epidermis. It also alters the plane of cell division in differentiating stomata. IAA at high concentrations (10⁻³, 10⁻⁴ m ), in combination with GA₃, overrides the effects of GA₃ on cell lengthening, while with low concentrations of IAA (10⁻⁹, 10⁻¹⁰m ), the effects of GA₃ are clearly dominant. At intermediate concentrations of IAA (10⁻⁶, 10⁻⁷m ), in the presence of GA₃, the effects of this treatment on cell differentiation closely parallel the pattern of differentiation in untreated tissue. It is postulated that a lateral gradient of auxin and gibberellin could control cell expansion in long epidermal cells during intercalary growth of the internode.     

DEVELOPMENTAL CHANGES IN THE KINETICS OF γ-AMINOBUTYRIC ACID TRANSPORT BY CHICK RETINA

—Isolated retinas from chick embryos and mature animals were incubated in [³H]GABA at 25°C for 10 min in order to investigate kinetic properties of the amino acid uptake system. Embryo retina accumulated [³H]GABA by two distinct kinetic systems with K_m values of the order 10⁻⁴m and 10⁻⁵m for the low- and high-affinity mechanisms respectively. However, as the retina matured, the high-affinity process disappeared and only the low-affinity system was detectable. No obvious explanation can be offered for this phenomenon although a similar observation has previously been made in chick brain by other workers.     

THE EFFECTS OF HORMONES UPON THE DEVELOPMENT OF EXCISED FLORAL BUDS OF AQUILEGIA

Young excised floral buds of Aquilegia were grown on defined medium containing kinetin, indoleacetic acid (IAA), or gibberellic acid (GA₃). Only when 10⁻⁶ or 10⁻⁷ m kinetin was added to the basal medium was there a significant increase in the number of initiated whorls of primordia. Buds on the basal medium or on medium with IAA or GA₃ failed to initiate carpels. On medium with 10⁻⁶ or 10⁻⁷ m kinetin, buds successfully initiated a normal whorl of five carpels. A high level of inorganic nitrogen was also required for the initiation of carpels. With 10⁻⁵ m kinetin, individual buds initiated from 6–18 carpels. Staminodial primordia of these buds were replaced with carpels, or the floral apex enlarged to accommodate a single whorl of many carpels. Kinetin did not support the further differentiation of the floral organs. Sepals, petals, and carpels did differentiate on medium with GA₃, but stamens aborted. However, on medium with GA₃ and kinetin, stamen primordia differentiated into short filaments and anthers. Further unknown growth factors appear to be required for the complete differentiation of floral primordia into mature organs.     

THE AFFINITY OF ONION CELL WALLS FOR CALCIUM IONS

Cell walls prepared from onion bulbs were found to exhibit an affinity for Ca⁺⁺. The adsorption of this ion was enhanced by the action of pectin methylesterase. It was confirmed that Ca⁺⁺ reacts with two COO“ groups and the corresponding affinity constant, K, was found to be: log K = 4.25. The action of pectin methylesterase had no effect upon K. The cell walls, as prepared, had 25 % of the total COO⁻ groups occupied by Ca⁺⁺, 14 % by Mg⁺⁺, and 39 % by H⁺. Treatment with acidified ethanol removed all of the metallic cations. K⁺ and Mg⁺⁺ could displace Ca⁺⁺ from the cell walls. At concentrations from 10⁻³ to 3 times 10⁻³ m it required from 4.9 to 13.2 moles of Mg⁺⁺ to displace one mole of Ca⁺⁺. For K⁺ it required 80 moles to displace 1 mole of Ca⁺⁺ at K⁺ concentrations from 0.65 × 10⁻² to 1.6 × 10⁻² M.     

Analysis of gamete and zygote motility in Allomyces

To study the mechanisms of chemotaxis in eukaryotes, the motility patterns of the gametes and zygotes and the chemotactic responses of the male gametes of the lower eukaryote Allomyces macrogynus were examined. Dark-field microscopy of the male gametes showed a smooth swimming pattern interrupted by very brief ‘jerks’ of the cell body that caused a change in swimming direction. Female gametes had a slower swimming velocity than the males and underwent more jerks or turns which accounted for their sluggish motility. The zygotes swam with the fastest velocity and were observed to have a helical swimming pattern involving a continuous turning of the cell body, a behavior absent from the gametes. Introduction of female gametes that produce the chemoattractant sirenin brought about an immediate change in the behavior of the male gametes. They moved in spirals (or helices) towards the source of the chemoattractant (the female gametes), undergoing only a few jerks to reorient the male cells. When very near the female cells, or in high concentrations of added sirenin, many very short motility tracks were observed that finally resulted in contact between the two gamete types. The results indicate that the poor swimming ability of the female gametes facilitates gamete contact, resulting in as many as 30–40 male gametes clustered on a single female cell. Further, male gamete orientation to the sirenin gradient is caused by the chemoattractant suppressing the jerk motion.     

Distinct regulation of two flagella by calcium during chemotaxis of male gametes in the brown alga Mutimo cylindricus (Cutleriaceae,Tilopteridales)

Brown algal male gametes show chemotaxis to the sex pheromone that is released from female gametes. The chemotactic behavior of the male gametes is controlled by the changes in the beating of two flagella known as the anterior and posterior flagellum. Our previous study using Mutimo cylindricus showed that the sex pheromone induced an increment in both the deflection angle of the anterior flagellum and sustained unilateral bend of the posterior flagellum, but the mechanisms regulating these two flagellar waveforms were not fully revealed. In this study, we analyzed the changes in swimming path and flagellar waveforms with a high-speed recording system under different calcium conditions. The extracellular Ca²⁺ concentration at 10⁻³ M caused an increment in the deflection angle of the anterior flagellum only when ionomycin was absent. No sustained unilateral bend of the posterior flagellum was induced either in the absence or presence of ionomycin in extracellular Ca²⁺ concentrations below 10⁻² M. Real-time Ca²⁺ imaging revealed that there is a spot near the basal part of anterior flagellum showing higher Ca²⁺ than in the other parts of the cell. The intensity of the spot slightly decreased when male gametes were treated with the sex pheromone. These results suggest that Ca²⁺-dependent changes in the anterior and posterior flagellum are regulated by distinct mechanisms and that the increase in the anterior flagellar deflection angle and sustained unilateral bend of the posterior flagellum may not be primarily induced by the Ca²⁺ concentration.     

PRODUCTIVITY OF PODOSTEMUM CERATOPHYLLUM IN THE NEW RIVER,VIRGINIA

Productivity of Podostemum ceratophyllum, the dominant aquatic macrophyte in the New River, was measured at four sites representing soft- and hardwater reaches of the river. Available dissolved inorganic carbon (DIC) was 4–5 times greater in the hardwater reach. The difference in available DIC was reflected in standing crop and productivity of P. ceratophyllum. Maximum standing crops of P. ceratophyllum at the two hardwater sites (Sites 1 and 2) were 244.8 ± 30.7 g ash-free dry wt (AFDW) m^−-2 and 193.8 ± 18.7 g AFDW m^−-2 compared to 128.5 ± 14.9 g AFDW m^−-2 and 101.3 ± 6.9 g AFDW m^−-2 for the softwater sites (Sites 3 and 4). Productivity, based on differences in standing crops, was: Site 1, 1.08 ± 0.12 g C m^−-2 d^−-1; Site 2, 0.86 ± 0.08 g Cm^−-2d^−-1; Site 3,0.58 ± 0.06 g C m^−-2 d^−-1; Site 4,0.45 ± 0.03 g C m^−-2 d^−-1. Corresponding values for productivity as ¹⁴C uptake were: 2.77 ± 0.44 g C m^−-2 d^−-1; 2.10 ± 0.45 g C m^−-2 d^−-1; 0.34 ± 0.04 g C m^−-2 d^−-1; 0.28 ± 0.03 g C m^−-2 d^−-1. Productivity/biomass (P/B) based on ¹⁴C uptake and standing crop revealed that P. ceratophyllum productivity was inhibited at the softwater sites perhaps due to carbon limitation. Because of its abundance and its high productivity, P. ceratophyllum is hypothesized to contribute significantly to the New River organic matter budget.     

THE EFFECTS OF KINETIN AND NAPHTHALENEACETIC ACID ON IN VITRO SHOOT MULTIPLICATION AND ROOTING IN THE FISHTAIL FERN

This study is concerned with the determination of the shoot and root inducing effects of kinetin (K) and naphthaleneacetic acid (NAA) on shoots ofthe fishtail fern (Nephrolepisfalcata formafurcans) in sterile tissue culture. The data shows that K is the major factor involved in maximal shoot production. The NAA is not essential. Specific concentrations ofNAA must be present with specific concentrations of K for maximal root production. At the same time, the data also demonstrate that shoots on media containing no NAA but with K concentrations of 5 × 10⁻⁷ and 10⁻⁶ M produced as many roots as with any other NAA concentration. The data can be used as a guide to rapid commercial propagation of fishtail fern, and demonstrate that media available commercially for Boston fern multiplication will induce maximal shoot production in fishtail fern.