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SUMMARYA model has been constructed to predict assimilation in four lichen species using climatological data. Gas exchange of the lichens has been measured in the laboratory in response to seasonal, light, temperature and moisture changes. By fitting polynomial equations to the response curves, the model predicts assimilation on the basis of these variables. A comparison of weight changes measured in the field with assimilation values predicted by the model using climatological data measured in the field, shows that the model gives realistic predictions over periods of 1 month. The model also permits the importance of the various environmental parameters to be examined, singly and in combination. Predicted assimilation values on climatically different days suggest that moisture is the single most important factor governing lichen growth -the assimilation gains during one rainy summer day can counteract the losses of five dry days. The model can now be extended to examine possible reasons for lichen distribution.

Fourteen sweet potato [Ipomoea batatas (L.) Lam] cultivars and varieties were examined for resistance to the sweetpotato weevil [Cylas formicarius elegantulus (Summers)] in artificially infested fields in Yoakum, TX. One cultivar W-226, appeared to have a greater level of resistance than the other cultivars examined. The data are compared to earlier resistance trials to show that the germplasm presently available has greater levels of resistance than that in previous years. The resistance levels of “Resisto” and “Regal” for the past 4 years are discussed.

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