Snmmary(1) Where grinding or maceration of plant tissue is impractical, immersion in methanoi should be used.(2) The adaption to aqueous methanol of existing techniques for distinguishing chlorophyll and phaeophytin in aqueous acetone was studied in detail. In methanol the spectra of both phaeophytin a and b were found to be pH sensitive. A method developed involving changes in absorbance at 665 nm is less precise than similar methods using acetone.(3) The spectra of phaeophytin b in methanoi at different pH levels are anomalous. Changes in absorbance between 440 and 410 nm cannot be used for the estimation of phaeophytin.(4) Plant pigments can be transferred from methanol to aqueous acetone without degradation of chlorophyll. Modified standard techniques may then be used to measure chlorophyll a and phaeophytin a content.
L An experimental study is described, designed to test the hypothesis that the loss of particles from suspension in flowing water follow.s an exponential decay function, the exponent of which is influenced more by water depth than water velocity. Successive experiments employed suspensions of Lycopodium spores which were introduced into one of the FBA's circulating channels maintained at its Waterston site, Dorset, under different combinations of water depth and pumping rate.2. In each experiment, the concentration of introduced spores indeed declined exponentially through time. The bulked, transformed data-set also conformed well to a single regression against a common time scale and which explained over 94% of the accumulated variances.3. The variance unexplained by the regression was apportioned among components distinguishing between experiments, experimental differences in starting concentration, water depth and pumping rate (veltKity). This analysis revealed that, after elimination of different initial concentrations, only water depth produced a significant effect, through its relation to the settling veU^ity of the Lycopodium. Thus, the hypothesis was not invalidated: water depth and not flow velocity proved to be the main controlling variable determining the rate of sinking loss in these experiments. Flow velocity is, nevertheless, an important component only in the sense that it influences the horizontal distance travelled by the residual spore suspension through the time period required for complete settlement.4. The consequences of experimental findings are applied to the maintenance of planktonic diatoms in rivers: both the survival of a potential growth inoculum and its downstream dispersion are strongly timedependent and are enhanced by greater channel depths.
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