Summary 2,4-Dinitrophenol, while increasing the respiration, inhibits the accumulation of ions by carrot cells. Further investigation is necessary to determine whether the inhibition is due to a direct effect of the dinitrophenol on the mechanism or whether the dinitrophenol indirectly prevents the mechanism from operating by causing some disorganization within the cell, possibly in the mitochondria. If the assumption that dinitrophenol inhibits phosphate transfers is justifiable, hypotheses of salt accumulation might require modification to allow for the participation of energy-rich phosphate. This would suggest that the Lundegardh mechanism may be a part of a more complex mechanism.

summary The freshwater macrophyte Hippuris vulgaris exhibits heterophylly. During July and August aerial‐type leaves occur even on immersed shoots down to a depth of 15 m in two clear‐water limestone lochs in Scotland. Complementary field and laboratory data indicate that a high intensity photoperiod and temperatures above 10°C are prerequisites for aerial‐type leaf production on submerged shoots. In these conditions, regular injections of additional sucrose, the natural photosynthate, at 05 mol kg−1 fresh weight will not induce the aerial‐type leaf. There is relatively little attenuation of blue light with depth in these lakes and additional blue light just after the photoperiod does not induce the aerial‐type leaf. There is no evidence for an ontogenetic or circadian photoperiodic requirement for the production of aerial‐type leaves, or that heterophylly is mediated by ethylene. However, a low ratio of red (R 660 run) to far red (FR 730 run) light throughout, or very dimly for a brief period just after, the photoperiod treatment regularly induces aerial leaf formation on submerged shoots of any length. A similar low R/FR ratio is found naturally in these lakes in summer at depths where submerged aerial leaves occur. Selective attenuation of far red by lakewaters raises the R/FR ratio steeply with increasing depth. At R/FR ratios above a critical range, which is similar in field and laboratory, aerial leaf formation is inhibited and only submerged‐type leaves are formed. Simply by changing the R/FR ratio, either during or briefly after the photoperiod, transitions between submerged and aerial‐type leaves are repeatedly reversible, implying direct phytochrome control.

Summary The freshwater angiosperm Potamogeton crispus produces specialized vegetative buds, known as turions, in early summer, in contrast to their autumn production by other temperate climate species. Laboratory experiments showed that turion production by P. crispus is triggered by long days (16 h or longer) and high temperatures (16 °C and above) together. Long days represent a photoperiodic signal apparently perceived by phytochrome. A midnight exposure to dim R light is necessary to induce turion formation in plants kept under short days, irrespective of total daily light dose. A single long day suffices to initiate turion formation. Under inductive long warm days few turions form at low photon fluence rates (whatever the total daily light dose) or at low R: FR ratios near 1 during the photoperiod. Rate and magnitude of turion production are greatly increased by increased photon fluence rates and R: F ratios above 1. Sucrose feeding hastens turion development, but turion initiation is not significantly altered. As predicted from experimental findings and natural lakewater photoperiods and temperatures, turions were observed on plants in lakes studied from June until August. Also, turions were confined as predicted to approximately the upper 15 m depth range in lakes where R: FR ratios and photon fluence rates were inductively high. Below these depths the R: FR ratio remains high but photon fluence rate is inadequate. Thus laboratory and field findings concur. In north temperate waters, turions of P. crispus appear to act as summer propagules which settle and germinate by autumn, rather than as overwintering hibernaculae.

SUMMARYConcentrations of the major component ions (K, Na and Cl) of sea water and cells of Enteromorpha intestinalis (L.) Link, were determined. Measurements of the electric potential difference across the plasmalemma and the influx and efflux of each ion indicate that K and Cl are actively imported and Na actively exported. Estimates of membrane permeability to the passive diffusive fluxes of these three ions alone have been used to explain the origin of the cell membrane potential. Tracer ion exchange kinetics are taken as showing that the tonoplast is more permeable than the plasmalemma to each ion.

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