Showing papers on "Shoot published in 1972"

Patterns in plant development

Abstract: Preface Acknowledgements 1. Development in the vascular plants 2. Embryogenesis: beginnings of development 3. Analytical and experimental studies of embryo development 4. The structure of the shoot apex 5. Analytical studies of the shoot apex 6. Experimental investigations on the shoot apex 7. Organogenesis in the shoot: leaf origin and position 8. Organogenesis in the shoot: determination of leaves and branches 9. Organogenesis in the shoot: later stages of leaf development 10. Determinate shoots: thorns and flowers 11. The development of the shoot system 12. The root 13. Differentiation of the plant body: the origin of pattern 14. Differentiation of the plant body: the elaboration of pattern 15. Secondary growth: the vascular cambium 16. Secondary growth: experimental studies on the cambium 17. Alternative patterns of development Credits Author index Subject index.

Uptake and Transport of Ions in Barley Seedlings III. Correlation Between Transport to the Shoot and Relative Growth Rate

Abstract: Determinations of potassium transport are described for plants growing at varied relative growth rates. These determinations were based on differences in total potassium content of the shoot over a 3.day period for plants growing on culture solution. It is shown that rate of transport from root to shoot is correlated with relative growth rate. The concentration of potassium in the shoot was independent of ratio of root to shoot, and little affected by relative growth rate (potassium was the only available univalent cation).

Germination and Seedling Development of Common Milkweed and Other Species

Abstract: Common milkweed (Asclepias syriaca L.) seed did not survive storage in water for 1, 2, and 12 months at 40, 30, and 5 C, respectively; but under dry storage seed viability was destroyed only at 40 C for 5 months. Stratifying common milkweed seed in water at 5 C was more effective in breaking dormancy than at 22 C. Mechanical scarification also caused a significant increase in germination. Exogenous 6-furfurylamino purine (kinetin) and gibberellic acid-3 (GA) increased germination while indole-3-acetic acid (IAA) had no effect. The optimum germination temperature scheme for common milkweed was an alternating 20 to 30 C, the maximum between 35 and 40 C, and the minimum between 15 and 20 C. Common milkweed seedlings were more susceptible to moisture stress than kochia [Kochia scoparia (L.) Schrad.] but less susceptible than hemp dogbane (Apocynum cannabinum L.) and sunflower (Helianthus annuus L.). In a greenhouse study common milkweed was less drought tolerant than eight other weed species. Common milkweed seedlings tolerated wider pH ranges than honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.], kochia, and sunflower. Common milkweed seedlings were less tolerant to salt solutions than four other species. Common milkweed emerged from 6-cm depths in Sharpsburg silty clay loam (sicl) at 20 or 30 C but only from the 3-cm depth at an alternating 20 to 30 C. Results from root box studies showed that common and honeyvine milkweed produced less shoot and root weight than kochia and sunflower and had a lower growth rate index of roots than sunflower. Common milkweed seedlings resprouted 21 days after planting when clipped at ground level. As days from planting to clipping increased, sprouting activity increased.

The interaction between growth promoters in apical dominance

Abstract: Summary Preliminary experiments with one-node cuttings of Solanum andigena in sterile culture indicated that residual root effects, possibly due to stored cytokinins, could obscure the effects of exogenous growth promoters on lateral bud growth in rootless cuttings. Therefore two-node cuttings, obtained from apical cuttings that had been maintained without roots for a number of days, were used in all subsequent investigations. Application of cytokinin or gibberellin to the base of rootless, two-node cuttings promoted the growth of lateral buds as leafy, orthotropic shoots, or diageotropic stolons, respectively; simultaneous application of both hormones completely inhibited lateral bud growth. The effects of roots, 6-benzylammopurine (BAP) and zeatin on lateral shoot growth were similar in leading to the formation of vigorous, orthotropic, leafy shoots. Indole-3-acetic acid (IAA) completely inhibited lateral bud growth in rootless cuttings for at least 7 days, even when BAP was included in the nutrient medium. By using [α-14C BAP it was demonstrated that cytokinin accumulates in the lateral buds of cuttings not treated with IAA, prior to their growth as leafy shoots; evidence of a causal relationship between cytokinin accumulation and lateral shoot growth was provided by a parallel experiment using [8-14C]-adenine. IAA did not appear to reduce BAP or BAP-riboside accumulation in lateral buds by diverting these cytokinins to the point of IAA application, but did promote the formation of an unknown metabolite of BAP which accumulated in stem tissue.

Seasonal variation in the composition of the volatile oil of the leaves, buds, and twigs of white spruce (Picea glauca)

Abstract: Gas chromatographic analysis of the volatile terpenes of the leaves, buds, and twigs of white spruce has confirmed that major changes take place only in the new shoots during the early part of summer. Minor changes were recorded for the older shoots during the same period. The relative amounts of β-pinene, limonene, and myrcene in the volatile oil of the buds change significantly during fall and winter. In contrast, the volatile oil of the leaves and twigs remains constant in quantitative composition during late summer, fall, and winter. The sequence in which the relative amounts of each terpene are laid down in the new growth is complex and no correlation with accepted biosynthetic pathways for monoterpenes could be found. During May substantial amounts of sesquiterpenes are present in the new growth, but these appear to be metabolized further as the summer progresses. The implications for chemosystematic studies are discussed.

The effect of environmental parameters on the germination, growth, and development of suaeda depressa (pursh) wats

Abstract: A study was made to determine the effect of environmental parameters on the germination, growth, and development of Suaeda depressa (Pursh) Wats. Germination tests showed that seeds germinated in solutions containing up to 4 % NaCl with no toxic effects indicated after treatment with distilled water. The rate of germination and the percentage germination decreased with increased salinity. The effect of environmental parameters on growth was measured by shoot height, side shoot development, leaf length, and dry weight. Growth was greatest in 1 % NaCl solutions with adequate available nitrogen. With increased salinity and low available nitrogen levels plant growth decreased. A 10-hr photoperiod stimulated immediate floral induction. Although flowering and completion of the life cycle occurred in solutions containing up to 4 % NaCl, increased salinity decreased the rate of floral induction and the dry weight of flowers and fruit produced. This study indicates that environmental parameters such as salinity, available nitrogen, and photoperiod can create a variety of growth forms, causing taxonomic confusion. SUAEDA DEPRESSA, an annual leafy succulent, is distributed west of the Mississippi River from southern Canada to Mexico. In this area, S. depressa is narrowly restricted to wet saline soils with poor drainage (Ungar and Capilupo, 1969). The restriction of certain species to saline environments was reported by Miller and Egler (1950) and Adams (1963). Coupland (1950) and Ungar (1964, 1965) concluded that distribution and zonation in saline soils was controlled by competition among species and individual tolerances to salinity. Laboratory studies by Binet (1963) indicated that S. vulgaris Moq. could grow under nonsaline conditions but made its best growth in 1.0 % NaCl nutrient solutions. The distribution of halophytes such as S. depressa is apparently controlled by soil salinity, with other edaphic and climatic factors playing a secondary role (Ungar and Capilupo, 1969). Gates, Stoddart, and Cook (1956) indicated that changes in the chemical factors of soils in saline areas were inconsistent with the distribution and zonation of the vegetation. Studies by Ungar (1968) and Ungar, Hogan, and McClelland (1969) showed that even though S. depressa most commonly occurred in heavy clay soils, the soil texture varied greatly and apparently had little influence on its distribution. Suaeda depressa has ' Received for publication 17 January 1972. 2 Present address: Department of Biological Sciences, University of Arizona, Tucson 85721. We wish to thank Dr. J. W. O'Leary and Dr. L. A. Larson for critically reading this manuscript. This research was partly supported by National Science Foundation research grant GB-6009. been found growing in soils ranging from 0.374.44 % in salinity, in which NaCl made up 93 % of the total salts (Ungar, 1968). Macroclimatic factors vary greatly along S. depressa's northsouth distributional axis and appear to have little significance in determining its distribution (Gleason and Cronquist, 1963). The purpose of this study was to observe the effects of different environmental conditions on the germination and growth of S. depressa. Specific attention was placed on height, branching, and leaf length and how they correlated with saline environments. METHODS AND MATERIALS-The seeds of Suaeda depressa were collected on October 3, 1964 at Cloud County, Kansas, and stored at 5 C until the initiation of the study in April 1970. There was no loss in viability over the storage period. Germination stludies-The seeds were germinated on two sheets of Whatman #2 filter paper in 100 mm x 15 mm petri dishes. All germination studies were initiated in the dark in 6 ml of distilled water with NaCl as noted. The results are based on 10 replicates of 25 seeds each for each test solution. Emergence and radicle growth to 0.5 cm in length were used as germination criteria. A temperature regime of 15 + 1 C for 14 hr and 5 + 1 C for 10 hr was used. This temperature regime was used to approximate the 11 C mean under natural conditions for April when seeds germinate in nature. All germination

Physiological Responses of Apple Trees to Supraoptimal Root Temperature

Abstract: Ungrafted apple rootstocks were grown in sand cultures at constant root temperatures between 20°C to 40°C. Temperatures of 30°C and above reduced root and shoot growth. Serious damage to the leaves occurred at 35°C and above. The O2 consumption, CO2 evolution and respiratory quotient (RQ) of the roots showed maximum values at 35°C. Different rootstock cultivars varied greatly in their susceptibility to damage by supraoptimal root temperatures apparently due to anaerobic respiration. The more susceptible ones differed from resistant types in the larger amount of ethanol they accumulated in their roots at supraoptimal root temperature, and the more severe reduction in the malic acid content of the roots at such temperature. Acetaldehyde was also found in roots and leaves at supraoptimal root temperatures, whereas the organic acid content of the leaves tended to decrease. Supraoptimal root temperature also caused a reduction of cytokinins in both roots and leaves accompanied by a reduction in the leaf chlorophyll content. This could be prevented by the application of kinetin or benzyladenine to the leaves. In a short experiment a rise in root temperature up to 40°C caused an increase in transpiration and a decrease in the resistance of the leaves to the passage of water vapor, whereas in prolonged experiments transpiration reached a maximum and leaf resistance a minimum at 30°C. The leaf water potential increased also with increasing root temperature. Leaf temperature increased with increasing root temperature, irrespective of increasing or decreasing transpiration rates.

The Regulatory Role of Inflorescence Leaves in Fruit‐setting by Sweet Orange (Citrus sinensis)

Abstract: Inflorescence leaves improve fruit set on sweet orange trees. We sought an explanation for this effect in terms of carbon demand by developing fruit versus potential supply from adjacent leaves. Our assessment was based upon measurements of fruit growth, leaf photosynthesis and 14C distribution patterns in plants grown under controlled conditions. Leafy inflorescences had sufficient foliar surface (1.24 dm2) and photosynthetic capacity (CO2 10.1 mg · dm-2· h-1) to support early development of fruits on the same shoot, and to make a substantial contribution towards subsequent growth. 14C-assimilates derived from new leaves were distributed towards adjacent fruit which showed strong competition for labelled substrate. By contrast, fruit borne on leafless inflorescences had to obtain all their assimilates from older leaves whose photosynthetic capacity (CO2 3.5–4.6 mg · dm-2· h-1) and individual area (0.2 dm2) were generally insufficient to wholly sustain fruit growth, so that a large number of old-leaves were needed; these fruit would be more susceptible to competition from other sinks.

The role of roots, cytokinins and apical dominance in the control of lateral shoot form in Solanum andigena

Abstract: The lateral bud of Solanum andigena has the potentiality to develop as a stolon or as a leafy, orthotropic shoot. Natural stolons are normally only produced from underground nodes, but aerial stolons can be induced to form by the application of a combination of indole-3-acetic acid and gibberellic acid (IAA/GA3) paste to the cut surface; under some conditions both natural or induced stolons are converted to upright, leafy shoots. The presence of roots was found to be necessary for the conversion of a natural stolon to a leafy shoot, but this root effect could be replaced by the synthetic cytokinin, 6-benzylaminopurine (BAP). By using α-14C-BAP it was demonstrated that cytokinin accumulates in the tip of an induced stolon, prior to its conversion to a leafy shoot caused by withdrawal of the IAA/GA3 paste. The application of IAA/GA3 to decapitated plants was shown to influence both the distribution and metabolism of the cytokinin. The possibility that the role of auxin in apical dominance, at least in part, is to control the distribution and metabolism of cytokinins is discussed.

Morphology and development of the primary and accessory buds of Eucalyptus regnans

Abstract: The vegetative axillary buds of Eucalyptus regnans F. Muell. at various ages were studied by light microscopy in serial sections and by direct observations in the field and glasshouse. All buds (except the very first apical bud) originated from axillary meristems, i.e. from generative tissue which arose in the axils of primordial leaves and survived in a meristematic condition for many years. Each axillary meristem normally produced one emergent primary bud and then an indefinite sequence of concealed accessory buds. The extensive dynamic shoot-system condensed within a primary bud comprised secondary as well as tertiary axes and their respective appendages. All parts were present throughout the year in a continuous sequence of maturation which extended also to the expanding shoot. During winter, development appeared to be merely slowed down or suspended. Primary buds which did not grow into shoots were shed after only a few weeks. The accessory buds were formed in a uniserial descending series at the base of and abaxial to each primary axillary bud. The first of the accessory buds was initiated within the primary bud, and the second within the expanding shoot. The first accessory bud resembled young primary buds in structure, but subsequent accessory buds were less and less complex. Keeping pace with the cambium, the axillary meristem formed a radial trace of thick-walled parenchyma in the wood and accessory buds embedded in a strand of thin-walled parenchyma in the bark. The distal portions of the bud strand and the buds embedded in it were shed progressively with the decorticating bark. Each of the bud strands which traversed the bark of 20-year-old E. viminalis Labill. was found to contain six to 12 radial strips of meristematic tissue. When epicormic growth was stimulated, several of these strips produced files of separate, new, condensed shoots. Of the scores of shoots thus initiated throughout the length of the bud strand, up to 10 or 20 of the distal ones emerged from the bark and grew into epicormic shoots. The buds of 20 other eucalypt species were examined by dissecting microscope only. It appeared that their bud systems were essentially similar to that of E. regnans. The widened concept of the axillary meristem shifts attention from individual buds to the continuous generative powers of the axillary meristem and helps to explain the outstanding capacity of the eucalypts to produce new shoots.

Effect of fungicides on the microflora of potato leaves

Abstract: The phylloplane flora of potato leaves was examined from the time of shoot emergence through to leaf senescence. Studies on untreated leaves have been combined with others in which the plants were sprayed using one of two fungicides currently in use for late blight control. Saprophytic fungi were in general found to be more susceptible to captafol than to maneb plus fentin acetate. Bacterial numbers were apparently unaltered by the spray treatments.

The photosynthetic capacity of stubble leaves and their contribution to growth of the lucerne plant after low level cutting

Abstract: The net carbon dioxide exchange rate (NCE) of lucerne (Medicago sativa cv. Hunter River) stubble leaves was found to be low (c. 55 ng CO2 cm-2 sec-1) immediately after removing shoots 15 cm above the stem base. However, within several days the NCE rose to a maximum of 130 ng CO2 cm-2 sec-1 on day 8. This peak rate was similar to that of recently expanded new leaves and held for about 3 days before declining. Leaves of similar age and position on uncut plants showed a steady decline in NCE. Leaf resistance, r'l, was low (c. 0.8 sec cm-1) and did not change as the NCE increased during the first 8 days. Mesophyll resistance, r'm, to carbon dioxide diffusion was initially high and declined from c. 9 to 2 sec cm-1 during this period. Comparison of dry weight changes of plant parts after stubble leaves were either retained or removed suggested that the tap-root benefited most by stubble leaf retention. The contribution to new shoots from stubble leaves appeared to be slight. However, when stubble leaves were exposed to 14CO2 on day 11, photosynthate was mainly exported into the shoot arising from the axil of the exposed leaf. This suggests that stubble leaves substitute, in part or completely, for the supply of carbohydrate to stubble shoots normally derived from reserves mobilized in the tap-root. The likely causes of rejuvenation in NCE of stubble leaves after partial shoot removal are discussed along with the significance of this photosynthetic contribution to regrowth of the lucerne plant.

Transport of Materials from the Cotyledons during Germination of Seeds of the Garden Pea (Pisum sativum L.)

Abstract: The transport of total dry matter, nitrogen, phosphorus, sulphur, potassium, and calcium from the cotyledons into the developing axis of young pea (Pisum sativum L.) seedlings has been studied under a variety of growth conditions. It is shown that the duration of transport increased when the plants were grown in distilled water, or in the dark, or upon removal of the shoot ; all these treatments delayed senescence of the cotyledons. On the other hand, the rate of transport was increased by treatments, such as the supply of calcium and phosphate in the medium, or darkness, which stimulate growth of the axis. Treatment of the seeds before germination with gibberellic acid (GA3) did not affect the movement of materials from the cotyledons although it changed the pattern of growth of the axis. After the first week of germination the relationship between the amounts of total dry matter, nitrogen, phosphorus, sulphur, and potassium transferred to the axis from the cotyledons in the intact plant remained approximately constant irrespective of the conditions of growth. It is proposed that the ratio in which the individual elements are transported is determined by the proportions in which they are released by the storage cells. Deviation from this ratio during the first week of germination, and over a longer period in deshooted plants is attributed to competition for the available nutrients between actively metabolizing cells in the cotyledons and axis. It is demonstrated by steam-girdling that movement of materials from the cotyledons into the shoot probably occurs via the phloem. Calcium is mobile in the phloem during the early stages of germination, possibly because the amount of free calcium in the cotyledons is high.

Shoot Growth and Mineral Composition of Leaves and Fruits of Apple as Affected by Relative Air Humidity

Abstract: Shoot growth and water consumption of potted Golden Delicious trees were studied under a controlled environment with respect to two levels of air humidity, soil moisture content, and the availability of nitrogen. In the high-N treatment, high air humidity and high soil moisture content promoted growth; at the iow-N level, growth did not respond to the treatments, Water consumption "w^as enhanced at low air humidity but was not affected by the moisture content of the soil. In potted fruit-bearing Cox's Orange Pippin trees exposed to two levels of air humidity, low humidity reduced shoot growth and, but to a much lower degree, fruit growth. It increased the spur-leaf levels of N, Mg, and, for part of the experimental period, K and Ca, but affected bardly the mmeral level in fruits. It is concluded that the amount of the minerals reaching the fruit is determined by the relative importance of tbe xylem influx during the first few weeks after fruit set and the phloem influx occurring throughout. It is. suggested that the xylem supply of the various minerals does not differ greatly; it is probably che main "way for the influx of Ca, but for N, K, Mg, and P the phloem influx is. completely dominating.

The effect of auxin from the shoot on root development in pisum sativum l.

Abstract: Summary The effect of auxin of shoot origin on the growth and development of the root system of Pisum sativum L. cv. Kelvedon Wonder was investigated. Root growth was reduced when auxin transport from shoot to root was interrupted, but this could have been caused by a reduction in assimilate supply rather than a deficiency of auxin. Shoot removal, however, markedly reduced the number and total length of secondary roots produced and a 1% IAA–lanolin paste applied to the cut stump compensated to a large extent for shoot removal, markedly increasing secondary root growth in de-shooted plants. It is suggested that auxin produced by the shoot may influence the growth and development of the root system.

Developmental studies on Euphorbia esula. The influence of the nitrogen supply on the correlative inhibition of root bud activity

Abstract: When seedlings of leafy spurge (Euphorbia esula L.) were grown at a low nitrogen level (10.5 ppm) the growth of the lateral buds on the shoot was completely arrested by apical dominance while the buds on the roots, although also inhibited, showed considerably greater activity. At a higher nitrogen level (210 ppm) apical dominance was markedly reduced but the resulting outgrowth of the lateral buds increased the inhibiting capacity of the shoot, limiting root bud response. When the main shoot was decapitated the degree to which root bud growth was suppressed by a given number of lateral shoots was inversely related to the nitrogen supply. Inhibition of the root buds by the lateral shoots could be significantly reduced by growing the plants initially at a low nitrogen level so that growth of the lateral buds was arrested. A subsequent increase in the nitrogen supply strongly promoted the growth of the roots buds, some of which were sufficiently released from inhibition to emerge as leafy shoots.

Gradients in the Nitrogenous Constituents of the Sap extracted from Apple Shoots of Different Ages

Abstract: A comparison was made of the nitrogenous constituents in the sap extracted under vacuum from apple shoots of different ages, as regards changes both with season and in response to fertilizer nitrate applied in summer or autumn. Before blossoming the N concentration of the sap changed markedly with age of shoot, with the values doubling in the samples from the proximal half of the 3-year-old wood to the distal 2-year-old section, followed by a significant decrease in the 1-year-old shoot. After blossoming the gradients in sap concentration were less pronounced but usually the lowest values were found in the youngest part of the shoot. Fourteen days after a soil application of nitrate in July there was a marked increase in the concentration of asparagine in the sap, but only in the 3-year-old section of the shoot. Seven days later the xylem sap from all parts of the shoot contained increased levels of asparagine, aspartic acid, and glutamine. No changes in the xylem sap of shoots in response to fertilizer applied in October were observed until the following April, Then increased amounts of asparagine and glutamine were found in all sections, with the greatest increase being seen in the youngest part. It is suggested that this was due to accelerated mobilization of N reserves into the xylem sap in response to growth regulators originating in the roots rather than to movement of recently

Studies on bud development in the rhizome of Agropyron repens. II. The effect of the nitrogen supply

Abstract: Bud growth on isolated rhizomes of Agropyron repens showed a basipetal gradient of decreasing activity and was strongly inhibited at the basal nodes. This evident polarity was correlated with a gradient of decreasing nitrogen content at successively older nodes and with an apparent translocation of nitrogen from the basal to the apical nodes. Isolating the buds from one another reduced growth of the apical buds and prolonged the growth of buds at the basal nodes so that the polarity of bud growth, although still apparent, was much reduced.Supplying nitrogen as NH4NO3 through the cut end of rhizomes still attached to the parent plant caused apical buds to develop as shoots instead of rhizomes. Increasing the nitrogen supply to the rooting medium extended this response to buds at older nodes, restricting rhizome production to basal buds whose growth was inhibited in low nitrogen rhizomes.Buds developing as shoots had a considerably higher total nitrogen and moisture content and a lower dry weight than buds ...

Shoot organization in vascular plants

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Observations on the Growth of Roots and Shoots of Tea (Camellia Sinensis, L.) in Southern Malawi

Abstract: SummaryThe construction of simple root observation trenches is described. Preliminary studies on the growth of roots and shoots of young clonal tea growing under irrigated field conditions in Southern Malawi showed that periods of maximum shoot growth were associated with minimal root growth. Observations on mature tea showed a high concentration of roots in the top 30 cm of soil but a marked reduction in active growth in this part of the profile during drought. Preliminary observations on mature tea showed a similar reduction in root growth during a period of intense shoot growth. Pruning of both newly planted and mature tea caused roots to cease growing for approximately three months. These observations are briefly discussed in relation to their probable effects on the uptake of water and nutrients

Changes in the Levels of Endogenous Growth Regulators during Development of the Flowers of Chrysanthemum morifolium

Abstract: Gibberellin-like substances and an auxin similar to IAA were detected by bioassays in extracts of flowers of Chrysanthemum nwrifolium. The activity of these substances was shown to reach a maximum early in the development of the flower when its relative growth-rate was at a maximum, and then to decline with the relative growth-rate. The leaves of lateral flowering shoots were found to contain gibberellins similar to those detected in the flowers while a different gibberellin, which appeared to decrease in activity with the age of the shoot, was detected in the stem. An auxin similar to indol-3yl-acetic acid (IAA) was also detected in these stems. Growth-promoting substances were not detected in the old stems and leaves from the main shoot. Gas-liquid chromatography revealed the presence of a number of additional gibberellins in the flowers. The chemical nature of the growth substances is discussed in relation to their biological and chromatographic behaviour.

Translocation of Shoot‐Applied Indolylacetic Acid into the Roots of Populus tremula

Abstract: Application of 10 to 100 μg indol-3-ylacetic acid to the leaves of rooted cuttings of aspen caused inhibition of root growth after three hours. Root growth recovered within 24 hours after IAA treatment. Swelling of the root tips occurred during the period of inhibition. The roots responded in the same way if IAA was applied in solution to the cut stem surface above the mature leaves. IAA-1-14C applied through a cut stem surface or to mature leaves was translocated downwards in the plants and labelled IAA could be isolated from the roots 3 to 24 hours after application. The ethanol-soluble activity decreased rapidly indicating a rapid metabolism or binding of IAA. IAA-1-14C applied to growing leaves was not translocated. From the rapid response of root growth it was concluded that IAA was translocated into the roots at a rate of about 7 cm per hour. This rate of translocation indicates that the sieve tubes are involved in the translocation. Implications of the results for the translocation of endogenous auxin into the roots are discussed.

Seasonal ionic fluctuations in a Phragmites communis community

Abstract: Calcium, magnesium, potassium, sodium, and phosphorus concentrations were measured in the shoots of a Phragmites communis community and its natural substrates during the growth season of 1969. Shoot length and shoot moisture were determined as indicators of physiological age. In addition, organic decay was followed by determination of the soil organic matter content and cation exchange capacity. Of the ions studied, calcium apparently increased in the shoot tissue, and magnesium, potassium, and phosphorus apparently decreased in the shoot tissue during the course of the growing season. Some speculations regarding the direction of net nutrient on flow in this community are advanced.

Effect of Ophiobolus graminis infection on the growth of wheat and barley

Abstract: SUMMARY Glasshouse experiments are reported, in which the development of young wheat and barley plants was examined following inoculation with Ophiobolus graminis (Sacc.) Sacc. The dry weight, leaf area, tiller number and water content of the shoot were reduced by infection. Reductions were equally severe in wheat and barley. The seminal root system of both was severely attacked and its growth retarded. Inoculated plants, however, translocated a greater proportion of their total assimilates to the root system and produced more adventitious roots than healthy plants. As a result there was an increase in both the number and proportion of healthy roots on these plants following the initial infection of their root systems. This effect was more pronounced in barley than in wheat. It is suggested that this may in part account for the reported relative tolerance of barley to take-all attack under field conditions.