Clear Lake, a small Canadian Shield lake that has been influenced little by human activity, was found to be more productive than expected from chemical and optical properties and geological surroundings. Production during the ice-free season ranged from 0.10 to 2.57 g C/m2 per day and averaged 250 g C/m2 per year for the lake as a whole. Other limnological factors studied (phytoplankton standing crop, oxygen, temperature, and nutrient regimes) were typical for an oligotrophic lake.The high production values are partially explained by the high correction for filtration error, which averaged 3.2 times for all occasions tested.Atmospheric precipitation is undoubtedly the major source of supply of the nutrients nitrogen and phosphorus to Clear Lake. Calcium and magnesium also appear to be largely carried in by precipitation, although most of the sodium, potassium, and silica entering the lake is weathered from the terrestrial watershed.

SUMMARYAustrian pine {Pimis nigra Arn.) and red pine {P. resijwso Ait.) were tested for needle damage caused hy sulphuric acid spray. Morphology and histology of newly grown needles were compared in 3-and 6-yr-old plants growing in the greenhouse under controlled conditions. Potted plants covered with plastic hags were sprayed daily either with distilled H^O or sulphuric acid of pH 2-5, 3-5 and 45. Needle tips, mid-parts and bases were fixed after 1, 3 and 24 h, and' 3, 7 and 30 d in glutaraldehyde-^0-1 % catTeine for intracellular precipitation of phenolics. Histoehemical reactions and electron microscopic observations showed that the morphological damage is linked to increased deposition of phenolic compounds in mesophyll cells, beginning directly under the stomata. Disorganization of membranes leads to death of the mesophyll cells, even before morphological damage i.s recognizable as brown spots on the needle surface. Thus the histoehemical reactions and observations of cell structure revealed damage earlier than macroscopic observations.

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In studies of Cronartium quercuum (Berk.) Miyabe ex Shirai, temperature and moisture conditions necessary for spore production, spore germination, and oak and pine infection were determined. Seasonal development studies then revealed that a series of favorable events was necessary for an inoculum "buildup" to occur on oak. Initial infection of oak by aeciospores resulted from at least 10 hours of saturated air accompanied by free water with the temperature between 8° and 28 °C. Late spring frosts and dry weather during aeciospore dissemination limited the spread. Secondary spread by urediospores was limited by dry weather and the decreasing susceptibility of oak leaves with age. The susceptible foliage produced by sprouts from recently cut oak stumps tended to prolong uredial spread. Infection of pine was only possible when viable teliospores were present on oak. During the years 1955–1958 in central Wisconsin they were present from the first week in June until the first of July if secondary spread by urediospores did not occur, or for about 2 weeks longer if secondary spread did take place. A period of at least 13 hours of 100% relative humidity following a measurable rainfall was necessary for production and germination of basidiospores. These conditions occurred infrequently and in some years not at all in central Wisconsin.

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