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Previous studies indicate that snowshoe hares (Lepusamericanus Erxleben) readily browse nursery-grown white spruce (Piceaglauca (Moench) Voss) seedlings but tend to avoid naturally regenerating juvenile trees. We confirmed these observations in feeding trials with snowshoe hares and investigated several possible explanations for this phenomenon. In vitro digestibilities of nursery-grown and naturally regenerating white spruce seedlings were similar, indicating similar contents of acid detergent fibre. Thus, it is unlikely that snowshoe hares are better able to extract nutrients from nursery-grown seedlings than from naturally regenerating white spruce. We suggest that snowshoe hares prefer to feed on nursery-grown seedlings because they contain less camphor (a specific compound in white spruce shown to deter feeding by hares) and have higher nutritional value (i.e., nitrogen) than naturally regenerating plants.

Spectroscopic measurements of the electron density and temperature have been made on a planar thermionic converter operated in the quasi-saturation region of the ignited mode. The effects of several independent converter variables on the electron density were investigated quantitatively. From this investigation it was found that the emitter temperature and current density were the most significant parameters affecting the electron density. Collector temperature, cesium vapor pressure, and interelectrode spacing were less important. Complete electron density profiles and electron temperature profiles were obtained and compared to conditions characteristic of local thermodynamic equilibrium (LTE). A representative case indicated the measured temperature, 2600°K, was only 200°K higher than required for complete LTE in the region of the peak electron density. This corresponds to an electron density approximately 45 percent below the equilibrium value.