Winter precipitation is defined as rain, dry fallout, and bulk precipitation—the last being a mixture of the other two. The division of winter precipitation into phases is based on collection procedures. Each phase shows distinctive characteristics of chemical composition. Rain displays the strong influence of the nearby Pacific Ocean and San Francisco Bay. Dry fallout, collected between rains, shows strong effects from locally derived materials in the atmosphere. Bulk precipitation shows, in chemical composition, the expected blending of the two environmental influences and is about 4 to nearly 10 times higher in mineral concentration than rainwater is. Bulk precipitation is considered the geochemically significant phase that should be used in studies relating contributions of atmospheric salts to surface‐ and groundwater supplies, to weathering, and to the nourishment of growing plants. Comparison with published data indicates that, wherever sampled, bulk precipitation contains more dissolved mineral content than rainwater does. Detailed comparisons, however, are not feasible because of widely differing procedures in sampling and analysis used in various studies. Increasing attention should be given to minor constituents in precipitation, as well as recognition of the several phases of precipitation.

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Warm-season yields of 14 C4-photosynthetic pathway tropical grasses were compared with yields of 6 Cg-pathway temperate grasses, and observations were made on the extent of flowering and on frost sensitivity. Plants were grown in mono culture in small swards at Palmerston North for two seasons. Plant spacing, cutting frequency and height, fertiliser dressings, and disease and pest control measures were selected to encourage each variety to express its growth potential both with and without irrigation. During the first season Setaria introductions produced the highest dry matter yields (14-16000 kg/ha); the temperate grasses yielded 8 500-12 000 kg/ha. : In the second summer Digitaria decumbens, Cynodon dactylon, Paspalum dilatatum, and Setaria splendida produced 16000-18000 kg/ha without irrigation and the temperate grasses 4250-12400 kg/ha. Tropical grasses yielded as well as or better than the temperate grasses during the warm season. Irrigation did not increase yields in the first summer. Only 4 out of 20 grasses yielded more under irrigation during the second summer. Tropical grasses had a wide range in sensitivity to late autumn frosts before all swards were covered with large plastic-covered frames for frost protection. Most Setaria introductions, paspalum, and three Digitaria lines flowered strongly in both seasons, whereas S. splendida, two Digitaria introductions, Pennisetum clandestinum, 'Grasslands Apanui' cocksfoot, and the ryegrasses flowered more profusely in the season after establishment.

;Paspalum dilatatum plants were grown in growth cabinets under two light intensities (224 and 90 W m-2) at day/night temperatures of 27.5/20.0, 20.0/12.5, 17.5/12.5 and 15.0/10.0°C. Additional plants were grown in the glasshouse and outside. Relative growth rate was closely correlated with the mean hourly photosynthetic rate of the plant during the day. Starch varied from 0.8 to 5.3 % of the leaf dry weight at the end of the night and from 3.0 to 11.6% at the end of the day. Photosynthetic rate of cabinet-grown plants remained constant during the day as starch accumulated. The rate declined for plants from outside, although their leaf starch levels were no higher than those of cabinet-grown plants. No evidence was found of feedback repression of photosynthetic rate caused by assimilate accumulation. There was only minor variation in mesophyll chloroplast structure between plants grown at different light intensities at the same temperature. A decline in temperature below 20.0/12.5°C increased swelling of mesophyll chloroplasts, as well as reducing development of the peripheral reticulum. The structure of bundle sheath chloroplasts was little affected by the environment apart from its effect on starch accumulation. While growth rate increased rapidly as temperature increased, there was much less effect of temperature on accumulation of starch during the day. It was concluded that photosynthesis and the accumulation of starch are less sensitive to temperature than is overall plant growth.

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