SummaryCalcium level in the substrate was found to have a very marked effect on the distribution of 45Ca in subterranean clover. Sites of initial accumulation of 45Ca included the vein endings along the distal margins of the leaflets, the lateral veins, and the proximal halves of the petioles.In plants with a normal calcium supply these sites were quickly saturated and the isotope became uniformly distributed in the lamina, which contained a higher concentration than its associated petiole. There was a positive correlation between leaf age and 45Ca concentration. In the petiole a somewhat higher concentration of 45Ca finally occurred in the distal when compared with the proximal half.Calcium-deficient plants differed in that, with the exception of the vein endings, the initial sites of accumulation of 45Ca were not rapidly saturated. In the lamina 45Ca moved into the interveinal tissues adjacent to the vein endings. Provided acute calcium-deficiency symptoms did not occur, there was finally a build-up of 45Ca in the distal half of the petiole. The concentration in the petiole was greater than in the lamina. Before runner-stem formation began there was not the same correlation in deficient plants between leaf age and nCa concentration as in nonnal plants, indicating that much of the newly absorbed 4SCa was acquired by young leaves of deficient plants at the expense of the oldest. This resulted in petiole collapse in old leaves due to the lack of build-up of calcium concentration in the distal halves of the petioles. The development of marginal necrosis of youngest leaves due to calcium deficiency was associated with a further disorganization of tSCa distribution. 4SCa accumulated in epidermal hairs and flowers.Translocation of 45Ca into new leaves and flowers produced up to 9 weeks after transfer from radioactive low-calcium solutions to non-radioactive normal· or lowcalcium solutions was demonstrated. This mobile calcium came mainly from root tissue.Cold water, hot water, hot 0'5N HCI, and hot 0'5% ammonium oxalate extracts were made of parts of leaves of different maturities from normal. and low-calcium plants sampled at two stages of growth, the first before and the second after the onset of -petiole collapse in the low-calcium plants. For all leaf parts, the cold water plus hot HCI extracts contained over 90% of the total 45Ca activity. For plants under normal calcium nutrition, the ratio of 45Ca soluble in cold water to that soluble in hot HCI was greater than 1, the ratio increasing with leaf age for all plant parts except the distal halves of the petioles. For plants under low-calcium nutrition, before the onset of deficiency symptoms, the above ratio, although lower in value, followed similar trends with leaf age as found in the normal-calcium tissues. Mter the onset of petiole collapse the ratio fell sharply to less than l.

Four water culture experiments are described in which the effects of the addition of all combinations of graduated amounts of phosphorus and zinc on the growth of subterranean clover were studied.In the first experiment, the variety Dwalganup was used, and in the other experiments the varieties Clare and Edenhope. Varietal differences in the symptoms of zinc deficiency are described. Phosphorus toxicity symptoms occurred in the variety Clare but not in Edenhope. The effects of increases in zinc or phosphorus level, or both, on growth of top + root (T + R) and on percentage top are described. A highly significant variety x phosphorus interaction effect on T + R was recorded at adequate zinc levels, which indicated that the phosphorus requirement of Edenhope was considerably greater than that of Clare. By contrast, tolerance to high levels of zinc in the substrate was greater in Clare than in Edenhope. In the presence of added phosphate, the initial T + R response to small, but still insufficient, additions of zinc to the substrate occurred in root growth more than in top growth, whereas when a level of zinc adequate for normal growth was supplied, top growth of the plants benefited more than root growth. Highly significant zinc x phosphorus interaction effects on T + R occurred. No relationship existed between zinc concentration and the occurrence of zinc deficiency symptoms. The critical zinc level was not a point of narrow range, but included a wide range of values, depending on the age of the plants and the phosphate level. The depression in T + R induced by high phosphate when the zinc level was insufficient was not due to a decrease in zinc concentration resulting from the high phosphate treatment, but such plants gave a high value for the phosphorus/zinc ratio. The results suggest that zinc is essential to phosphate utilization by the plant. Evidence of redistribution of phosphorus from tops to roots, and of decreases in the total amount of phosphorus in phosphorus-deficient plants, was obtained in one experiment between days 27 and 60.

SummaryA series of water-culture experiments was conducted with broad bean (Vicia faba L.), common stock (Mathiola incana R. Br.), subterranean clover (Trifolium Bubterraneum L.), and garden peas (PiBum Bativum L.) grown in normal-and lowcalcium nutrient solutions. Leaves of the plants were either injected or s,,!rfacetreated with an aqueous solution of 45CaCh with and without various additions to the dose. The subsequent distribution of 45Ca in the plants was determined by means of radioautographs and radioassays.In each species, where nothing was added to the dose, there was negligible movement of 45Ca from the treated leaf. With broad bean or common stock or both, the addition of small amounts of EDTA (disodium salt) or HCI or both, or of citric acid, caused marked movement of 45Ca in an acropetal direction in both the normal and calcium-deficient plants. Marked accumulation of 45Ca occurred in the epidermal hairs and anthers of common stock. There was also some evidence of retranslocation of 45Ca in this species.A series of experiments with subterranean clover confirmed the effect of EDTA in promoting mobility of 45Ca when either injected into a leaf or applied to the uninjured leaf surface. With low concentrations of EDTA, movement was mainly acropetal, but with a high concentration marked basipetal movement to the roots also occurred.When graduated amounts of non-radioactive calcium (as CaCh.6H20) or equivalent amounts of magnesium (as MgCh.6H20) were added to the dose, increasing mobility of the injected 45Ca occurred in both normal and calcium-deficient plants. With the highest levels of calcium or magnesium additions, movement of 45Ca occurred throughout the plant including the cotyledons and the whole of the root system.

The results of a series of water culture experiments is reported in which the comparative effects of summer or winter conditions respectively on the growth of subterranean clover (Trifolium subterraneum L. var. Dwalganup), red clover (T. pratense L. certified), white clover (T. repens L. 'mother strain' certified), cluster clover (T. glomeratum L.), suckling clover (T. dubium Sibth.), and barrel medio (Medicago tribuloides Desr. strain 173), in a complete nutrient solution and in solutions deficient in either potassium, phosphorus, or magnesium were studied. In the complete nutrient solution, the mean daily increment in dry weight (T+R) for each species was less in winter than in summer. Rates of growth (T+R) of red clover, white clover, cluster clover, and suckling clover were each reduced more by winter as compared with summer conditions than was that of barrel medic, while a similar comparison also showed that white clover and suckling clover were more affected than subterranean clover. For subterranean clover and barrel medic (T+R) differed little as between the summer and winter tests respectively, but (T+R) for red clover, white clover, cluster clover, and suckling clover was significantly depressed under winter conditions. Significant season X species interactions occurred. Differences in seasonal conditions had no effect on the percentage top of five of the species when grown in the complete nutrient solution, but in the sixth species (barrel medic) winter conditions when compared with summer conditions favoured top growth at the expense of root growth (i.e. increased percentage top). Within any species there was no significant seasonal effect on the depression in (T+R) caused by a deficiency of either potassium, phosphorus, or magnesium. Between species certain significant effects were unrelated to seasonal conditions for potassium or phosphorus deficiencies, but with magnesium deficiency significant species x season interactions occurred for (T+R). Within species, the mean effect of potassium deficiency in reducing percentage top in all tests was significant for white clover, barrel medic, and suckling clover, but the season x potassium level interaction was significant for cluster clover only. There were no significant differences between species. Phosphorus deficiency caused a significant reduction in percentage top within all species under both summer and winter conditions, but no significant season x phosphate level interaction occurred. The percentage top of white clover was reduced more than that of subterranean clover in summer, but not in winter. Magnesium deficiency produced a significant reduction in the percentage top of white clover and barrel medic in winter, but not in summer. The season x magnesium level interaction effect was significant for white clover. Several significant species x magnesium level interactions for percentage top were also recorded.

Data on the occurrence of deadheads in wheat have been collected in agronomy trials In Victoria over many pars. The main points arising from this data are- 1. No consistent differences in the susceptibility of many commonly grown Australian varieties. 2. No positive relationship between a root rot index and the number of deadheads. 3. A significant reduction in deadhead numbers with the use of superphosphate in half the fertilizer trials where counts were made. In other trials, where superphosphate had no significant effect, the general trend was still a reduction in deadheads where superphosphate was used. 4. In several trials, deadheads increased after a pasture period. Barley grass was a prominent species in many of the pastures and, in others, legume species were an important component. In some trials there were more deadheads where barley was included in the rotation and, in others, less deadheads where oats were included. 5. In general, there was an increase in deadheads when fallowing was delayed, especially if the initial working was not done until just before sowing. 6. Burning stubble, when the land was winter-fallowed, did not significantly, affect the number of deadheads.