Phase Change in Hedera helix: Induction of the Mature to Juvenile Phase Change by Gibberellin A3

A sensitive and reproducible method to obtain GA₃ induced morphological reversion of mature Hedera helix to the juvenile form has been developed. Dose response experiments indicate that GA₃ stimulates reversion over a 50–100 fold range with a half maximal response at approximately 0.5 μg GA₃ per plant. The individual characteristics involved in phase change revert to the juvenile form in a sequential manner as GA₃ dose is increased. Variations in light intensity from 1.2–3.6 × 10⁴ lux and temperature from 15 to 26°C do not affect this hormonal response. Other growth regulators including indoleacetic acid, kinetin, abscisic acid and (2-chloroethyl)phosphonic acid (Ethephon) are inactive but other gibberellins (GA₁ and a mixture of A₄–A₇) are active in stimulating reversion. Therefore, the response is specific for gibberellins as a class of hormones but non-specific for a particular form of gibberellin. The significance of this response in relation to juvenility in woody plants is discussed.     

Respiratory Mechanisms in the Aroid Spadix

The flowers of Skunk-cabbage (Symplocarpus foetidus), like thespadix tissues of other Aroids, have a rapid, carbon monoxideand cyanide (HCN) resistant respiration; oxygen uptake is independentof the oxygen partial pressure over a wide range. Cell fractionswere isolated by differential centrifugation and their oxidativeactivities studied. Oxidation of succinate and citrate by mitochondriacan be inhibited 50 to 60 per cent. by 1 X 10^–3 M. HCN,and antimycin A (AA) causes partial inhibitions. An active mitochondrialcytochrome-c oxidase is present, and it shows a typical sensitivityto cyanide. The mitochondria possess an active reduced diphosphopyridine-nucleotide(DPNH) oxidase system, which is inhibited roughly 80 per cent.by 1 X 10^–3 M. HCN and 1.7 µg./ml. AA. The microsomalDPNH oxidase, which is less sensitive to inhibitors, is lessactive per gramme of tissue than that on the mitochondria. Thefinal supernatant shows little DPNH oxidase. With all fractions,reduced triphosphopyridine nucleotide (TPNH) is oxidized muchmore slowly than DPNH. DPNH-cyto-chrome-c reductase activitywas measured; the mitochondrial system is partially blockedby AA, whereas the microsomal activity is AA-insensitive. Spectro-photometricexamination of a preparation of solubilized mitochondria showedthat cytochromes a, b, and c are present. The results are discussedwith reference to the pathway and localization of hydrogen andelectron transport in the Aroid spadix.     

Use of additive models to represent trends in a barley field trial

Even when a field experiment has been designed with care, subsequent examination of the plot values may reveal additional unforeseen trends. In this paper we examine data from a barley pathology field trial and show that additive models provide a flexible representation of environmental trends, in one or two dimensions. Such models smooth out noise in the observed data, rather than fit an equation specified in advance. This approach tends to increase the precision of treatment comparisons relative to a classical analysis of variance. We recommend the use of residual plots to explore experimental data for underlying trends, and additive models to display these trends and estimate treatment effects.     

Earthworm communities in conventional wheat monocropping and low-input wheat-clover intercropping systems

A comparative study was conducted on earthworm communities in a conventional winter wheat monocropping system and a low‐input intercropping system in which successive crops of winter wheat were direct‐drilled into a permanent white clover sward. Earthworm abundance, biomass and species composition under the two cropping systems in the second and third years of successive cropping were assessed each spring and autumn in farm‐scale field plots at four sites using formalin and electrical extraction methods. The wheat‐clover cropping system supported larger earthworm communities (overall mean abundance 548 individuals m^?2, 137 g biomass m^?2) than conventional wheat monocropping (194 individuals m‐2, 36 g biomass m‐2). Between one and five more earthworm species were recorded in the wheat‐clover system than in the wheat system at three out of the four study sites. Wheat–clover cropping especially favoured species belonging to the epigeic and epigeic/anecic ecological groups such as Lumbricus castaneus, L. festivus, L. rubellus, juvenile Lumbricus and Satchellius mammalis. Earthworm communities in the wheat‐clover cropping system were comparable in size and species composition to communities normally found in perennial grassland‐type habitats such as pastures and grass‐legume leys.     

Distribution of Soluble 14C-Labelled Assimilates as Related to Distribution of 14C-Benzyladenine in Shoot Tips of Hedera helix

The relationship between benzyladenine and assimilate distributions in shoot tips of English Ivy (Hedera helix L.) was studied. Exogenous applications of benzyladenine resulted in small amounts of the hormone moving to the apical meristem. The large part of the recovered benzyladenine was found in the young leaves of the shoot tip. Benzyladenine increased the amount of ¹⁴C-labelled assimilates in the shoot tip, but the distribution pattern of those assimilates within the tip was like that of the untreated control.     

A Method for Determining the Position and Size of Lateral Primordia in the Axes of Roots Without Sectioning

A procedure for staining, clearing, and mounting the axis ofa root is described which permits rapid measurement of the longitudinaland radial position and the length and diameter of each lateralprimordium therein.     

Relationship between canopy reflectance and yield loss due to disease in barley

Reflectance from barley field trial plots was measured to determine whether it could be used as an accurate estimate of disease and yield response to fungicide, and whether this was consistent over a range of agronomic factors. Three trials were used to test the effects of cultivar, assessment date, fungicide and dose, different disease and fertiliser. Correlations with predominant disease and resulting yield loss were high, often better than visual disease or green leaf area measurements alone. Certain ratios of two reflectance wavelength measurements were more robust predictors than single wavelengths. Cultivar and development stage had a large influence on measurements and calibration for such morphology-based characters would be essential for practical deployment. Whilst weather conditions and solar angle restrict opportunities for usage of reflectance tools such as the‘Cropscan Radiometer', it may prove useful in crop loss assessments as an additional objective tool.