The Diffusion of Carbon Dioxide and Water Vapour through Stomata

An account is given of the diffusion of carbon dioxide and ofwater vapour through the stomata of leaves in the presence ofair. It shows that the argument given in K. J. Parkinson andH. L. Penman's paper (1970): ‘A Possible Source of Errorin the Estimation of Stomatal Resistance’ is substantiallyincorrect. However, the correction factors to the sugar beetdata presented in their paper are valid owing to a fortuitousset of circumstances including the similarity in magnitude oftwo mutual diffusion coefficients. The concept of stomatal resistanceis criticized.     

压电石英晶体免疫传感器

近年来压电石英晶体免疫传感器作为一种新型生物传感器发展迅速,该文对其检测原理、材料选择、振荡模式选择及再生使用进行了详细介绍,并介绍了其在微生物检测、病毒和蛋白质检测,环境监测方面的具体应用。     

Water Vapour Calibration using Salt Hydrate Transitions

There is a thermodynamic equilibrium between hydrate pairs ofa salt and the water vapour pressure of the surrounding gas.The vapour pressure depends on the nature of the salt hydratepair and on the salt temperature. It is shown that the transitionof ferrous sulphate from the heptahydrate to the tetrahydratewill humidify flowing gas to this equilibrium vapour pressure,provided that the gas is in contact with the crystals for about12 s. The relationship between the equilibrium water vapourpressure and crystal temperature has been established over therange 10–40 ?C (with an accuracy of ?0-1 ?C at 16 ?C).At 20 ?C the equilibrium relative humidity is 55.8%. A practical humidity calibrator based on this hydrate transitionhas been built and tested. Using two-way valves, the input supplyof dry air is divided so that part goes to the exit directly,and the rest to the exit via a ferrous sulphate column maintainedat a constant and measured temperature. By varying the fractionpassing through the ferrous sulphate, the humidity of the emergentair may be varied between zero and the humidity in equilibriumwith the ferrous sulphate.     

Vapour action of fungicides against powdery mildews

Certain fungicides prevented the growth of powdery mildews at distances extending several millimetres beyond the edge of localized deposits on leaves. Most of the materials also acted at a distance when separated from the leaf by glass cover-slips, indicating that the effect was due to the emission of vapour. In addition to sulphur and lime-sulphur, whose vapour action is already known, fungicides based on drazoxolon, oxythioquinox, binap-acryl, dinitro-octyl phenyl crotonates and a phthalimido-phosphonothionate were found to act in this way. Two systemic fungicides, griseofulvin and triamiphos, did not give a detectable vapour action. Tests were conducted mostly on open glasshouse benches. A draught from a fan shifted the zones of inhibition to one side of the deposits, but did not reduce their areas. Vapour effects were similar in extent on plants maintained at 18–25° C and at 27–32° C. Variation in the areas protected was studied in relation to the size and fungicide content of the deposits, to different powdery mildews, to time of incubation and to different types of formulation. Deposits applied to leaves by high- or low-volume sprays at concentrations used in the field gave significant protection at a distance. Vapour effects were demonstrated also on mildew conidia incubated on glass slides bearing a spot of fungicide, and on infected plants placed in beakers coated on the bottom with fungicide. Movement of fungicides in the gaseous state is discussed in relation to the control of foliage diseases in the field.     

Quartz tuning fork biosensor.

The use of quartz tuning forks for biosensor applications is investigated. The basis of the sensor is to coat the tuning fork surfaces with specific biomolecules and measure subsequent mass loading from the selective binding of complementary analytes. Two experimental set-ups are evaluated, direct mechanical excitation and self-excitation. Mechanical excitation is achieved by mounting the fork on a piezoelectric plate and it is found that the change in oscillation amplitude on adsorption can be monitored to give the change in mass. However, a major drawback is that the sensitivity is determined by the Q-factor, which varies significantly between different sensors and different experimental arrangements. In self-excitation mode, tuning fork motion is activated and detected by placing the fork within a tuned circuit. Using self-excitation mode, anti-human IgG modified tuning forks can sense the binding of human IgG in the range of 5-100 microg ml(-1). The significance of this study is that quartz tuning forks are routinely made using standard microfabrication process, thus suggesting the possibility of facile microfabrication of arrays of quartz sensors.     

The Importance of Water Vapour for the Circulating Air Flow through Nelumbo nucifera

Aquatic vascular plants depend on an adequate oxygen supplyin order to maintain growth and reproduction in anaerobic environments.Nelumbo nucifera is able to survive with a gas transport systemwhich supplies oxygen to the roots and rhizomes submerged inthe anaerobic sediment. It was possible to demonstrate thatthis gas transport system is based on a purely physical phenomenonThermo-osmotic oxygen transport was first demonstrated on freshleaves with the help of an oxygen-sensitive electrode. A definiteenhancement of oxygen flow was obtained through excised leaveswhen a temperature difference between the ambient and lacunarair was present in light. These leaves were then dried to brittlenessand the enhanced oxygen flow was still detectable. This showsthat not only photosynthetic oxygen, but also atmospheric oxygencan be transported to the buried organs. The absolute flow ofoxygen through dry leaves was much lower than through freshleaves, but the thermo-osmotic transport of oxygen still functioned.Furthermore, the process of thermo-osmosis need not rely ona difference in humidity between the two sides of a porous partition,but may be linked causally to the temperature difference andthe pore size. Key words: Nelumbo nucifera, oxygen transport, thermo-osmosis of gases     

The Use of Vapour Fixation for the Investigation of Fully Hydrated Living Plant Material

The screening of possible candidates for vapour fixation formicrogravity experiments indicated that the only useful agentswere acrolein and formaldehyde. Acrolein, alone or in combinationwith formaldehyde, gives consistently good preservation of non-vacuolatecells with good cytoplasmic detail. Formaldehyde also producesgood preservation. In highly vacuolate cells plasmolysis occursand is probably unavoidable in vapour fixation. The duration of fixation can be varied considerably withoutgross differences in the fixation image. The identification of a successful inactivation procedure meansthat acrolein vapour fixation has the potential to be appliedin practice. Acrolein, aldehydes, vapour fixation, Arabidopsis thaliana, microgravity, space biology     

The Role of Quartz in the Origin of Optical Activity on Earth

A thorough analysis of literature data on distribution of rightand left quartz in many locations on the surface of Earthindicates that quartz enantiomorph crystals are distributed inequal amounts in all locations. Therefore optically activequartz crystals of one or the other enantiomorph could not serveas the source of homochirality in the evolution of biosphere.Hence the calculation of a PVED based on published `small excessof left quartz crystals' on Earth lacks a sound physical basis.