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Artificial neural networks are capable of learning and are potentially superior to other computer programs at pattern recognition. We have used a simple two-layer, feed-forward neural network to obtain structural information from IR spectra of organic compounds. The network was taught to recognize the presence and absence of selected functional groups and bond types by simply presenting it with I R spectra of training compounds. The back-propagation algorithm was used to adjust the weights of the network. Spectra of compounds not belonging to the training set were used for testing. The trained network was able to recognize the presence and absence of the functional groups and bond types in the spectra of previously unseen compounds. Percent transmittance vs. wavenumber was the most successful input data representation. Using both bond type and functional group identification in the output layer significantly reduced the number of incorrect classifications.

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The variability in thickness of the O and A2 horizons was studied on a sandy loam forest soil in the Great Lakes‐St. Lawrence Region of southern Ontario. Horizon thicknesses were recorded in 1.3 cm (0.5 inch) classes for each 10.2 cm (4 inches) of horizontal distance on the faces of each soilpit. Soilpits were located both subjectively on windthrows and randomly in the study area. Thickness frequency distributions for O horizons were normal and for the A2 horizons Poisson‐like. Both were independent of recent fire history and sampling method. It may be inferred that the disturbance by windthrow is infrequent in relation to O horizon formation, but frequent relative to A2 horizon development. Microtopographic position had a slight effect; thicknesses in top positions being somewhat less than for bottom positions. Horizon distortions related to windthrow disturbance were recorded for only 19% of the soil profiles sampled.

The acetylene‐reducing activity of excised root nodules of Myrica asplenifolia L. [Comptonia peregrina (L.) Coult.] was measured on a large number of samples both in the field and in the laboratory. The apparent Km for acetylene was determined to be 0.006 atm and was not significantly different in the presence or in the absence of 0.8 atm of N2. Maximum activity was obtained between 26 and 30C and between 0.15 and 0.25 atm O2. No significant diurnal fluctuation in activity could be detected. High variation (coefficient of variation ca. 50%) between replicate samples of field‐collected nodules was a consistent feature of estimates of acetylene‐reducing activity over a range of sites, sample weights, and sample numbers. Therefore, field‐collected nodules are unsuitable for physiological experiments unless the effect of the treatments on acetylene‐reducing activity is large. In ecological studies where field‐collected nodules must be used, extensive sampling is required to permit reliable estimates of the activity. The ratio of the rate of ethylene produced from acetylene to the rate of 15N2 incorporated was measured by exposing individual nodule samples sequentially to 15N2, then acetylene. The mean ratio for 24 samples was 3.14 ± 0.30.