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The growing concerns over desertification have spurred research into technologies aimed at acquiring water from nontraditional sources such as dew, fog, and water vapor. Some of the most promising developments have focused on improving designs to collect water from fog. However, the absence of a shared framework to predict, measure, and compare the water collection efficiencies of new prototypes is becoming a major obstacle to progress in the field. We address this problem by providing a general theory to design efficient fog collectors as well as a concrete experimental protocol to furnish our theory with all the necessary parameters to quantify the effective water collection efficiency. We show in particular that multilayer collectors are required for high fog collection efficiency and that all efficient designs are found within a narrow range of mesh porosity. We support our conclusions with measurements on simple multilayer harp collectors.

Morphogenesis of plant cells is tantamount to the shaping of the stiff cell wall that surrounds them. To this end, these cells integrate two concomitant processes: 1), deposition of new material into the existing wall, and 2), mechanical deformation of this material by the turgor pressure. However, due to uncertainty regarding the mechanisms that coordinate these processes, existing models typically adopt a limiting case in which either one or the other dictates morphogenesis. In this report, we formulate a simple mechanism in pollen tubes by which deposition causes turnover of cell wall cross-links, thereby facilitating mechanical deformation. Accordingly, deposition and mechanics are coupled and are both integral aspects of the morphogenetic process. Among the key experimental qualifications of this model are: its ability to precisely reproduce the morphologies of pollen tubes; its prediction of the growth oscillations exhibited by rapidly growing pollen tubes; and its prediction of the observed phase relationships between variables such as wall thickness, cell morphology, and growth rate within oscillatory cells. In short, the model captures the rich phenomenology of pollen tube morphogenesis and has implications for other plant cell types.

The dasycladalean algae produce diverse whorled structures, among which the best known are the vegetative and reproductive whorls of Acetabularia acetabulum . In this paper, we review the literature pertaining to the origin of these structures. The question is addressed in terms of the necessary patternforming events and the possible mechanisms involved, an outlook we call the pattern formation viewpoint. The pattern–forming events involved in the morphogenesis of the vegetative and reproductive whorls of Acetabularia have been used to define five and six morphogenetic stages, respectively. We discuss three published mechanisms which account, at least in part, for the pattern–forming events. The mechanisms are mechanical buckling of the cell wall, reaction–diffusion of morphogen molecules along the cell membrane, and mechanochemical interactions between Ca2ions and the cytoskeleton in the cytosol. The numerous differences between these mechanisms provide experimental grounds to test their validity. To date, the results of these experiments point towards reaction–diffusion as the most likely patterning mechanism. Finally, we consider the evolutionary origin of the vegetative and reproductive whorls and provide mechanistic explanations for some of the major evolutionary advances.

In tip-growing plant cells such as pollen tubes and root hairs, surface expansion is confined to the cell apex. Vesicles containing pectic cell wall material are delivered to this apical region to provide the material necessarily to build the expanding cell wall. Quantification of wall expansion reveals that the surface expansion rates are not highest at the pole but instead in an annular region around the pole. These findings raise the question of the precise localization of exocytosis events in these cells. Recently, we used spatio-temporal image correlation spectroscopy (STICS) in combination with high temporal resolution confocal imaging to characterize the intracellular movement of vesicles in growing pollen tubes. These observations, together with the analysis of FRAP (fluorescence recovery after photobleaching) experiments, indicate that exocytosis is likely to occur predominantly in the same annular region where wall expansion rates are greatest. Therefore, tip growth in plant cells does not seem to happen exactly at the tip.