Vertical temperature gradients between instrument shelter and plant heights were investigated. A sample of 160 lapse rate observations was taken during the growing season. Concomitant observations of date, time of day, plant cover, soil type, sky cover, wind speed, and thermodynamic air mass classification were also made. Means and sources of variation for the lapse rates were examined.

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* Journal Paper No. J-1700 of the Iowa Agricultural Experiment Station, Ames, Iowa, Project 996 in cooperation with the USDA, Crop Disease Forecasting Project through partial support by funds of the Research Marketing Act of 1946. Taken from a thesis presented to the Graduate Faculty of the Iowa State College in partial fulfillment of the requirements for the degree of Master of Science.

1 Agent, Division of Mycology and Disease Survey, USDA. The author wishes to express his gratitude to Prof. H. C. S. Thorn and Dr. J. R. Wallin for aid in the initiation and accomplishment of the investigation. Thanks are also due to Prof. O. Kempthorne for help in the analysis of the results.