Rates of respiration and dry matter accumulation were measured for growing squares (floral buds), bolls, and leaves of cotton, Gossypium hirsutum L. After assuming a “maintenance respiration” and a “growth respiration”, it was possible to derive an equation whereby such components of respiration could be estimated from regression analysis of transformed experimental data. New values for the efficiency of conversion of photosynthate into dry matter were estimated for leaves, squares and bolls; such values ranged from 50 to 69%. The theory, experiments described, and results from cotton offer hope for better descriptions of respiration for growing organs of other plant species. Such information is urgently needed for the development of management models depending on predictions on effects of environment on plant growth.

‘Bluebelle’ cultivar of Oryza sativa L. was grown in a growth chamber at 4 and 16, 10 and 21, 16 and 27, and 21 and 33C night (10 hr) and day (14 hr) temperatures, respectively. Flood water was applied 12 (early) or 24 (late) days after seedling emergence at 6- and 12-cm depths to seedlings growing in saline, alkaline, and normal Crowley silt loam soil. Plant tops were harvested 53 days after seedling emergence and analyzed for dry matter production and composition of P, K, Mg, Na, Fe, Mn, and Zn. Water samples were collected at the soil-water interface 1, 2, 5, 7, 8, 9, 10, 11, 14, and 15 days after soedling emergence and analyzed for pH, electrical conductivity, CO₃⁻, HCO₃⁻, and C1⁻. When temperature was increased, the order of dry matter production by plants growing in the various soils was normal > saline > alkaline. Applying flood water 12 days after seedling emergence caused plants growing in saline and normal soils to produce more dry matter, whereas those growing in alkaline soil produced more dry matter when flooded 24 days after seedling emergence. Varying flood depth did not affect growth. Plants growing on saline and alkaline soils at 21 and 27C were chlorotic and P/Zn was less than 1.0. When temperature was increased to 31C chlorosis disappeared and P/Zn was greater than 1.0; however, the data did not explain the effects of flood time on growth. Bicarbonate level of water above the alkaline soil was higher when flooding was delayed. This suggested young seedlings were more sensitive to HCO₃⁻ than were older seedlings, since growth was greater with delayed flooding. Flooding saline soil early produced lower EC and Cl⁻ values in the water than did late flooding. Thus, plants grew more when flooded early because salinity was lower.

Leaf water potential, fruit water potential and leaf infiltration scores were used as indices of the plant water status of three apple varieties, during one growing season. The highest and lowest leaf water potentials recorded, during the early morning period, were respectively for Delicious .9 atm and -20 atm, Jonathan -3.5 atm and -19 atm, and Granny Smith -4 atm and -13 atm. Mean fruit water potential was similar for Granny Smith and Delicious, but considerably lower for Jonathan. Leaf infiltration scores and leaf water potential maintained a close relationship, while leaf and fruit water potentials showed considerable divergence. These data serve to show the magnitude of plant water stress which apple trees have to contend with in an almost normal growing season in Queensland.

The results of testing lucerne for resistance to the stem nematode Ditylenchus dipsaci are recorded. A major part of the study was given to perfecting a technique for growing lucerne seedlings for inoculation with nematodes. Two techniques were tried and filter paper rolls were found to be superior to soil flats. The technique of growing seedlings in filter paper rolls and inoculating them with nematodes was used to produce a rating of the resistance for the New Zealand variety of lucerne, Wairau, when compared with a known resistant variety, Washoe and a susceptible variety, Grimm. From the results obtained Wairau must be classified as a susceptible variety. It appears that a selection within a variety of lucerne for resistance to Ditylenchus dipsaci could be made by eliminating the swollen plants. However, to obtain the relative resistances of several varieties, it would be necessary to obtain a measure of the reproductive rates of the nematodes in the plants.