Resistance to Water Loss from the Mesophyll Cell Surface in Plant Leaves

A method is described for the accurate measurement of the apparentresistance to water loss from the mesophyll cell walls of plantleaves (r_w), and for studying the mechanism underlying thisresistance. The method for distinguishing possible mechanismsinvolves a comparison of the calculated values of r_w at differentrates of evaporation. The value of r_w remained below 50 s m^–1at relative water contents greater than 11 ± 3% and 7± 2% for Pelargonium hortorum Bailey and Vicia faba L.respectively. Therefore r_w is relatively insignificant at normalphysiological water contents in these species. When r_w did increaseit was not sensitive to evaporation rate, suggesting that alowering of the vapour pressure at the evaporating sites wasnot involved. This contrasted with the results for cellulosefilter paper, where r_w was more sensitive to evaporative flux.     

Empirical models of the conductance of leaves in apple orchards

Abstract. Seasonal data on leaf conductance (g_l) for three different apple cultivars grown in four separate orchards with different aged trees was studied between 1979 and 1985. A number of empirical models for predicting leaf conductance from environmental measurements were compared using this data and a general method for adapting such models for the prediction of different data sets is proposed. Although stepwise multiple regression identified relative humidity or vapour pressure as important variables, it frequently did not identify the optimal set of independent variables, which often did not include either of these. There was no advantage in regressing g_l against principal components of the environment, rather than against the raw environmental variables. A simple model involving air vapour pressure deficit, air temperature and a hyperbolic function of irradiance was found to explain between 32 and 62% of the variance in g_l for the different data sets. Parameters fitted for one data set led to the effective prediction of g_l in other years or plots. The model fit could generally be improved significantly by including soil moisture deficit among the independent variables.     

Caste and colony variations in the chemical composition of the cephalic secretions of the African weaver ant, Oecophylla longinoda

ABSTRACT. Considerable differences were found in the composition of the volatile cephalic chemical of the castes of Oecophylla longinoda. The mandibular glands of minor workers contain a series of primary alcohols, predominantly 1-hexanol, 1-octanol and 1-nonanol, together with nerol and geraniol. Hexanal, 2-butyl-2-octenal and 3-undecanone (components of the mandibular gland secretion of major workers, and which are important stimuli in alarm communication) are absent. Major workers are attracted and arrested by high concentrations of nerol, which is part of a possible mechanism for communication within the nest. The heads of males contain a pungent secretion, which may be used in defence; the major constituents are five aliphatic acids. The quantities of both main and trace constituents of the mandibular gland secretion of major workers were found to vary between colonies collected in different areas of West Africa.