Seed Discharge in Arceuthobium: A Photographic Study
Photographs, made at a speed of 5 microseconds, of the ejection of the Arceuthobium seed from its fruit, show that tumbling in the vertical plane begins soon after discharge and that most seeds have turned 90 degrees when they have traveled about 6 centimeters. As the seeds leave the fruit they have a viscous sheath around the trailing end that disintegrates after the seeds have traveled about 2 to 3 centimeters. This viscous material does not act as a rudder as has been postulated.
Thermogenesis-triggered seed dispersal in dwarf mistletoe
Lodgepole pine dwarf mistletoe (DM), Arceuthobium americanum, is a parasitic flowering plant and forest pathogen in North America. Seed dispersal in DM occurs by explosive discharge. Notably, slight warming of ripe DM fruit in the laboratory can trigger explosions. Previously, we showed that alternative oxidase, a protein involved in endogenous heat production (thermogenesis) in plants, is present in DM fruit. These observations have led us to investigate if thermogenesis induces discharge. Here, infrared thermographs reveal that ripe DM fruits display an anomalous increase in surface temperature by an average of 2.1±0.8 °C over an average time of 103±29 s (n=9, 95% confidence interval) before dehiscence. Furthermore, both non-isothermal and isothermal modulated differential scanning calorimetry consistently show an exothermic event (~1 J g−1) in the non-reversible heat flow just prior to discharge. These results support thermogenesis-triggered seed discharge, never before observed in any plant.
Compact Circularly Polarized Composite Cavity-Backed Crossed Dipole for GPS Applications
In this paper, we present a circularly polarized (CP) composite cavity-backed crossed dipole antenna for global positioning system (GPS) applications. We produce the CP radiation by crossing two dipoles through a 90° phase delay line of a vacant-quarter printed ring, which also has a broadband impedance matching characteristic. Two techniques, insertion of meander lines in the dipole arm and arrowhead-shaped trace at its end, are employed to reduce the sizes of the primary radiation element. The compact radiator is backed by a cavity reflector to achieve a wide CP radiation beamwidth. The proposed antenna exhibits a measured bandwidth of 1.450～1.656 GHz for a voltage standing wave ratio (VSWR) < 2 and 1.555～1.605 GHz for AR < 3-dB. At 1.575 GHz, the antenna has a gain of 7 dBic, a frontto-back ratio of 27 dB, AR of 1.18 dB, and 3-dB AR beamwidths of 130° and 132° in the x-z and y-z planes, respectively.