Leaf Fatty-Acid Content in Relation to Hardening and Chilling Injury

At 25?C the leaves of chill-resistant plants did not containmore unsaturated fatty acid than chill-sensitive plants. Furthermorewhen chill-sensitive plants were hardened at 12?C there wasno increase in the amount of unsaturated fatty acid or totalweight of fatty acid in the leaf. These results cast furtherdoubt on the importance of the degree of unsaturation of thefatty acids in determining the critical temperature at whichthe phase change occurs in the lipid portion of the membrane. When chill-sensitive plants are chilled (5?C) the percentageof linolenic acid and total weight of fatty acid decreases rapidlybut remains constant in chill-resistant species. Hardening mayreduce the degree of damage to the plant by slowing down detrimentalprocesses such as the decrease in the percentage of linolenicacid which occurs on chilling.     

Alcohol Dehydrogenase Activity in Relation to Flooding Tolerance in Roots

The ability of a number of plants to grow under conditions ofexperimental flooding has been examined. There was an increasein ethanol production under anaerobic conditions in those specieswhose growth was reduced by flooding. The period of floodinginduced a marked increase in alcohol dehydrogenase activityof the roots of these plants. Plants not adversely affectedby flooding showed no increase in ethanol production and noinduction of alcohol dehydrogenase activity. It is suggestedthat species in which such activation occurs are excluded fromwet areas because of the accumulation of toxic quantities ofethanol.     

Comparative Morphology of Echinoderm Sperm and Possible Phylogenetic Implications

The sperm morphology of at least 7 crinoids, 11 ophiuroids,23 asteroids, 23 holothuroids, and 37 echinoids is known. Forall the known crinoids, ophiuroids, and asteroids, the spermare spherical, while those of echinoids are conical. Holothuroidsperm are basically spherical, with two exceptions: cylindricalin Cucumaria lubrica and tabloid in Cucumaria pseudocurata.The possible implications of sperm morphology in the mode offertilization and in echinoderm phylogeny are discussed.     

Air-surface exchange measurement in heterogeneous regions: extending tower observations with spatial structure observed from small aircraft

Strategies to assess long-term atmosphere-ecosystem exchange of CO₂ and H₂O must deal not only with time trends but also with spatial variability. Flux towers efficiently measure time trends, but only at discrete sites, always limited in number. Representativeness of these sites and the causes of spatial variation between sites are difficult to investigate from tower data alone. Such issues are better addressed with flux measurements from moving vehicles, particularly aircraft. Recent technological advancements in aircraft and instrumentation now allow mobile flux measurement with enhanced precision, greater ease, and lower cost. Results are presented which illustrate the importance of spatial variability, and some suggestions are given for assessment of flux-tower representativeness. Unfortunately, airborne observations of the kind presented here are practical only during a part of the daylight hours in brief intensive field campaigns. Extrapolation of spatial-structure information derived from these measurements to night-time or to long-term averages thus remains problematic. For the foreseeable future this extrapolation will require models that faithfully simulate both space and time characteristics of H₂O and CO₂ exchange. The development and validation of such models will be greatly enhanced by the increased availability of measurements from moving vehicles, which record spatial as well as temporal structure.