Patterns of stem development in late spring/summer regrowths after initial cuts at three growth stages are described. The stages at which the initial cuts were taken were: (a) before stem apices were raised to defoliation level (5 cm), (b) two weeks later when the apices of about 90% of the stem tillers were raised above this height, and (c) four weeks after (a), when the apices of all stem tillers were raised well above cutting height.

Following an initial cut at stage (a) stem development was quickly resumed, the most advanced tillers being devoid of leaf blades. After initial cuts at the later stages there was virtually no stem development until after the fourth week of regrowth.

The greater proportion of stem tillers in the earlier regrowth was not reflected in reduced digestibility during the first six weeks from cutting.

Reproductive (apical) development was generally weak in tillers in which stems developed in midsummer (after cutting at stages b and c); at least two-thirds of these tillers were indeterminate.

The significance of the distinct batch of stem tillers developing in spring is discussed, and the data are also considered in relation to (i) avoiding stemmy regrowths in spring, (ii) stem development and herbage quality, and (iii) summer stem extension and the perennation of the sward.

Three short-term experiments on green-manuring are described. In the first, trefoil (T) and ryegrass given fertilizer N (RN) increased the yield of a following barley crop grown without fertilizer N by 500–900 kg/ha, but did not affect yield of barley given N. In the second, T and RN increased yield by 1400 kg/ha whether or not fertilizer N was given to the barley. Ryegrass without fertilizer N (R) had smaller effects in both experiments. The third experiment (with different treatments) suggested that the effect of trefoil was caused by the greenstuff turned in, not by any physical or microbiological change in the soil.

Growth rates, chemical composition of the body and wool production were measured with wethers and ewes from two genotypes of sheep grazing at two planes of nutrition. The nutritional treatments were applied after weaning at 12 kg live weight. Animals were slaughtered at 6 kg intervals between 12 and 54 kg live weight.

Dorset Horn × (Border Leicester × Merino) lambs grew 57% faster than South Australian Merino lambs before weaning, produced 22% more wool and contained more fat at weaning.

Post-weaning growth rates on the high and low planes of nutrition were 168 and 78g/day for Merinos and 183 and 116 g/day for Cross-breds. Despite these differences, there was virtually no effect on body composition. Sheep which were starved and re-grown also had a similar body composition to sheep grown continuously.

There was, however, a nutritional effect on wool production. On the high plane of nutrition the rate of wool production was 22% higher than on the low plane of nutrition.

After weaning there were only small differences in the growth rate of the two genotypes but the Merinos grew 30% more wool than Cross-breds on the high plane of nutrition and 39% more wool on the low plane of nutrition. Genotype differences in the fat and protein content of the empty body were small, but Merinos contained more ash, Ca, P and Mg.

After weaning the normal pattern of allometric growth was reversed; at 18 kg live weight the sheep contained a lower proportion of fat and higher proportion of water than at 12 kg live weight. Above 18 kg live weight normal allometric growth was resumed. The fat-free empty body became progressively less hydrated but the ratio of protein: ash remained constant at 79:21 for Merinos and 81:19 for Cross-breds.

There was a trend towards ewes being fatter than wethers, but this was only significant with Merinos. Other sex differences in body composition, body growth and wool growth were not significant.

Scottish Blackface ewes were used to investigate the effect of protein deficiency during pregnancy on serum albumin, globulin, transferrin and plasma urea concentrations. Twenty-eight sheep were offered one of two iso-caloric diets in amounts which maintained energy intake at levels comparable to those found in hill sheep during winter. For half of the sheep (HP group) the crude-protein concentration was 11·8% and for the remainder (LP group) 6·0% in the dry matter. A further six sheep (group CL) were offered a diet containing 16·0% crude protein in amounts which prevented undernutrition. Concurrent changes in plasma volume and in certain serum proteins during pregnancy were determined in a second experiment.

Serum globulins were not affected by protein intake and fell from 44·5 to 30·7 mg/ml during pregnancy. This was attributed mainly to a 30% increase in plasma volume which occurred during pregnancy.

Serum albumin concentrations at the end of pregnancy were 29·3, 22·0 and 17'7 mg/ml and serum transferrin concentrations 400, 307 and 300 mg/100 ml in the CL, HP and LP groups respectively. Initial mean albumin and transferrin concentrations were 28·0 mg/ml and 383 mg/100 ml respectively. The usefulness of the parameters as indices of the protein status of pregnant ewes was discussed.

Plasma urea N concentrations were related to the current protein intake of the animal. Mean values during late pregnancy were 26·0, 7'4 and 4·0 mg urea N/100 ml in the CL, HP, and LP) groups respectively. Limitations as to its usefulness were discussed.

Four growth regulators were tested: N-dimethylaminosuccinamic acid (aminozide); N-pyrrolidinosuccinamic acid (F529); 2-chloroethyldimethyldodecylammonium chloride (JF2579); potassium 2(3-chlorophenylcarbamoyloxy) propionate (JF3072); all shortened stems. JF2579 and JF3072 were phytotoxic and lessened yield. Aminozide and F529 (tested in 1970 only) did not affect yield in 1970 but aminozide increased yield by 28% in 1971. Seed rates and row spacings had small effects on yield which varied with season. Growth regulators did not interact with seed rates or row spacing. Plant density and growth regulators had effects on yield via the number of stems and pods per stem. The effects of season on yield were greater and were caused via 100 grain weight. Speculative hypotheses are suggested to explain the different actions of season and treatments.

Several alternative statistical approaches to the analysis of genotype-environment interactions are summarized, and their inter-relationships are presented mathematically and graphically. An experiment was designed to test the ability of these analyses to satisfactorily describe genotype-environment interactions and to locate genotypes causing or contributing significantly to such interactions in a situation where environments differed in only one factor, i.e. soil nitrogen status.

Twenty-five lines of wheat were grown at each of 5 levels of applied nitrogen (0–270 kg N/ha) in a sandy, nitrogen-deficient soil, and their grain yields and yield components (ears per unit area, grains per ear, weight per grain) were determined. Designating the nitrogen levels as ‘environments’, linear yield responses, and deviations from linear responses, of individual wheat entries to environment mean yield were calculated according to the various statistical procedures previously outlined. The results suggested that the linear response to environment mean yield was similar for all wheat entries. However, further inspection of the data revealed that the responses of eight entries to environment mean yield departed significantly from linearity. Although several analyses satisfactorily identified these aberrant entries, classifying them as ‘unstable’, it was concluded that the degree of departure from linearity of response was not an adequate measure of instability. Furthermore, as previously suggested by Knight (1970), it was confirmed that the relative ranking of an entry for yield stability according to such a concept varied according to the average response of the group of entries with which it was being compared.

The general effects of applied nitrogen on yield components were to increase the number of ears and the number of grains per ear, and to decrease grain weight. However, only the first of these effects occurred consistently for all entries. The number and weight of individual grains per ear varied with the nitrogen treatment, often unpredictably, in a complex pattern which differed significantly between entries.

An experiment comparing six-course rotations which included 1-, 2- and 3-year leys of pure grass, pure legume and grass/legume mixture is described, and the results from the fifth and sixth phases of the first cycle and first and second phases of the second cycle are discussed.

Compared with all-arable cropping, the inclusion of leys increased the yield of barley grown as the second and third crops after the leys were ploughed up, although the difference was less when 58 kg N/ha had been applied. Neither length nor type of ley affected yield in the second crop after ploughing the leys, but in the third crop 2- and 3-year leys led to greater yield than 1-year leys.

Only rotations containing 1-year leys were compared with all-arable cropping in the fourth and fifth crops after ley, but some effects of these were still apparent in that both Italian ryegrass and broad red clover leys led to an increased sugar percentage of sugar beet grown as the fourth crop when no nitrogen was applied, and broad red clover leys led to a greater response to nitrogen in barley grown as the fifth crop after ley.

Experiments were done to determine the fate of soluble mucins in the gastrointestinal tract of sheep. Incubation of a soluble mucin with liquor from large intestinal contents resulted in loss of mucin. Some of this loss was due to soluble enzymes. The loss of mucin was less when incubation was with rumen liquor and variable when with ileal liquor.

The mean amounts of nitrogen in a soluble mucin fraction which was soluble in trichloroacetic acid (T.C.A.-soluble mucin) were 2·5, 7·3 and 20·0 mg per 100 ml in rumen caecal and faecal liquors respectively. These amounts were only a small proportion of the total soluble nitrogen in these fluids.

Amounts of T.C.A.-soluble mucin, measured by sugar content, were greatest in contents from the small intestine. When the amounts of T.C.A.-soluble mucin were compared with the amounts of lignin in the samples, there was an increase between the abomasum and the first part of the small intestine and then a decrease to the caecum. Amounts relative to lignin were low in other parts of the gastro-intestinal tract.

The greatest ratio of fucose to rhamnose in T.C.A.-soluble mucin from gastro-intestinal liquors was in ileal liquor. The presence of the two methyl pentoses, fucose and rhamnose, indicates that the T.C.A.-soluble mucin is derived from mucus and bacteria.

Four of five ‘hairy’ Wiltshire lambs had fibre type arrays (as defined by Dry, 1965) of Plateau (P0 and P1) type, whereas in five ‘woolly’ lambs there was only one Plateau (P3) array, the arrays of the remaining lambs being Ravine or Saddle. In terms of Dry's theory that the severity of pre-natal check determines persistence of wool growth in adults, it appears that the amount of checking in these Saddle and Ravine arrays was insufficient to prevent the casting of the adult coat.

Four digestibility and balance experiments were carried out in which 33 growing heifers were fed basal diets of low dry matter silage offered ad libitum, supplemented with various levels of barley and/or groundnut meal or urea.

Voluntary intake of the silages was low although apparent digestibility of D.M. was high (66–75%). There was a significant linear negative relationship between the intake of D.M. as supplement and silage D.M. intake.

Apparent digestibility of crude fibre in the silages was high (74–83%). It was depressed significantly by addition of barley but not by addition of groundnut. There was a highly significant linear relationship between the digestibility of D.M. and G.B. in the mixed silage concentrate diets used.

Metabolizable energy (M.E.) values for the silages varied from 2·04 to 2·52 Mcal/kg (8·5–10·5 MJ/kg) D.M. Supplementation with barley at approximately 1% of live weight, increased M.E. values of the mixed diets to 2·57–2·85 Mcal/kg (10·8–11·9 MJ/kg) D.M. Additional N had little effect on these values.

Nitrogen retention was significantly increased in all experiments by barley supplementation. It was further significantly increased by groundnut in three experiments and by urea in one experiment.

Multiple regression analysis showed that N retention was significantly related to both M.E. intake and intake of absorbed N, and to M.E. intake and intake of supplementary N.

Apparent availabilities of Ca and Mg in silage based diets were low and the availability of Na varied with Na intake. Supplementation with either energy or nitrogen increased apparent availability and retention of Mg but did not exert consistent effects on availability or retention of Ca or Na.

There was a highly significant linear relationship between ingested and digested Na but not for Ca or Mg. There was a highly significant linear relationship between absorbed and retained Ca and Mg, but not for Na.

Animals fed second cut silages had rather low blood glucose levels and higher than normal levels of blood ketones.

Experiments were carried out to assess the effects of silage diets given with and without supplementary energy as barley and/or nitrogen as groundnut meal or urea on rumen fermentation in growing heifers.

Silage based diets resulted in a stable pH and a high molar percentage of acetate in rumen liquor. Total V.F.A. concentrations were significantly increased by supplementary energy plus protein but were not consistently increased by energy only, and were linearly related to M.E. intake but not to D.M. digestibility. Effects of energy and nitrogen supplementation on the molar percentage of rumen V.F.A. were small and not always significant.

Rumen NH3-N levels were normal on the basal silage diets and were linearly related to N intake. Levels were significantly reduced by energy supplementation but significantly increased by protein supplementation. Results are discussed in relation to energy and nitrogen utilization on silage based diets.

Forty-four full-sib families from a diallel cross between 10 Lolium ((multiflorum × perenne) × perenne) clones were planted in the autumn at 0·6 × 0·6 m and 0·l × 0·l m spacings. Fresh weight of individual plants was measured on three occasions during the following spring and summer. The analysis of the diallel cross was extended to account for combining ability × spacing interactions, and to estimate between-spacing combining ability correlations and their sampling errors.

Family × spacing interactions became increasingly significant at successive harvests and always contributed substantially to the total phenotypic variance. Much of the family × spacing variance was due to the general combining ability (GCA) × spacing component. Despite these large and significant interactions, the correlation between GCA values at the two spacings was high and positive at each harvest, so that selection for yield at wide spacing should lead to a correlated increase in yield at close spacing. Although the experiment was of relatively short duration, the results suggest that recent criticism of the conventional technique of selection among widely spaced plants in pasture plant breeding programmes may not have been entirely justified.

The mean yield of field beans grown for three consecutive years on a site infested with migratory nematodes was 1540 kg grain/ha in untreated soil and 1870 kg/ha in soil treated with dazomet.

Fertilizer nitrogen in amounts up to 250 kg N/ha decreased yield to 990 kg in untreated soil but increased it to 2220 kg in soil treated with dazomet. Fertilizer nitrogen did not affect nematode numbers or root blackening but decreased nodulation and increased mycorrhizal infection by Endogone sp. in untreated soil. Dazomet greatly decreased migratory nematodes of the genera Tylenchorhynchus and Trichodorus and eliminated Pratylenchus. It had little effect on root blackening in the top 10 cm of soil but decreased it in the next 10 cm. Infection with Endogone was almost eliminated.

The optimal intensity of P supply for lettuce was investigated in a pot experiment with five soils, six levels of P application (0, 15, 30, 60, 120, 240 ppm) and three times of harvest (2, 3 and 4 weeks after emergence). The P adsorption isotherm for each soil was measured in 0.01 M CaCl2.

All soils responded strongly to P application, the amounts required for maximum growth varying from 120 ppm on a sandy soil to 300 ppm on a moss peat. The differences in requirement were related to the P adsorption by the soil, and on all soils a solution P concentration of about 1 ppm resulted in maximum growth.

The Optimal leaf P concentration in young lettuce was about 0·6%.

Ten varieties of field beans, grown in different environments, were analyzed for genotypic stability of their seed yield. The linear responses to the environments were insignificant, but deviations from linearity were highly significant suggesting that the relatively unpredictable component of the genotype x environments interactions was more important in this material than the relatively predictable component. Environmental effects per se were very important in determining differences in mean seed yield. The relatively large deviations from linearity of variety IW may be due to powdery mildew disease. RB 29 was identified as a good yielding and stable variety in the range of environments tested.

The skeletons of 34 pigs killed at a number of weights from birth to 120 kg were examined radiographically. Data were also used from radiographs of 83 foetuses of different ages.

Estimates were made of the age of appearance of various ossification centres and measurements taken of the diaphyseal length and breadth. A chart is given showing the age of appearance of ossification centres. Exponential equations in which the independent variate was time were fitted to both pre- and post-natal linear measurements. These equations were used to calculate the age at which each of the measurements attained a given proportion of the post-natal asymptote. The development of the pig's skeleton is discussed in relation to that of other species. Attention is drawn to the possibility that the uncritical use of accepted terminology such as early and late maturing may tend to obscure an understanding of the manner in which certain components of the skeleton develop.

Populations of spaced plants of each of the four American upland cotton varieties Deltapine Smooth Leaf, Rex Smooth Leaf, Pope, and Rex and one African upland variety, Bar 7/8, were grown in the 1965–6 wet season at Kimberley Research Station, in the Ord River valley, Western Australia. The number of bolls, boll weight, lint percentage, seed cotton yield, lint yield, micronaire value, mature height, and morphological type were recorded for each plant.

For all varieties the range of each attribute was wide; for example, for a typicalvariety, boll weight ranged from 3·0 to 7·8 g, lint percentage from 30·5 to 43·5%, micronaire value from 3·3 to 5·9 units, and mature height from 78 to 195 cm.

The most variable varieties judged on coefficients of variation were those maintained at the station for the longest period without selection while the most recent accession was the least variable.

Frequency distributions for all attributes in each population departed significantly from normality: the majority showed both significant skewness and kurtosis. Positive skewness shown for the yield parameters seed-cotton yield, lint yield, boll number and boll weight in all varieties suggested there was scope for improvement by selection. Negative skewness for lint percentage was found in three varieties, suggesting previous intense selection for this trait. The coefficient of variation of lint percentage with one variety (Deltapine Smooth Leaf) was considerably less than that recorded 30 years earlier for its predecessor D x PL 11 A.

Covariance adjustments to seed cotton yield of individual plants, based on various hypotheses of the relationship between a plant's yield and that of its neighbours failed to give reductions of consequence in the variability of yield. It was concluded that inter-plant influences were far more complex than the models assumed.

Progenies of randomly chosen plants from spaced plant populations of four American and one African variety of Gossypium hirsutum L. were grown in replicated single-plant plots at Kimberley Research Station in 1967–68 (all varieties) and 1968–9 (two varieties only) to estimate intra-varietal parameters of genetic variability.

Estimates of broad-sense heritability were usually similar when derived from components of variance on either a one- or two-season analysis basis or by parentprogeny regression Heritabilities were in general lowest for lint yield and boll number and highest for lint percentage. Mean value of heritability for lint yield and boll number, considered consistent enough on a varietal and seasonal basis to allow averaging, was about 0·15. Components of variance estimates of heritability on a single environment basis for other attributes ranged as follows: boll weight from 0·05 to 0·56, lint percentage from 0·29 to 0·80, mature height from 0·00 to 0·51, micronaire value from 0·20 to 0·63 and Pressley strength index from 0·05 to 0·56.

Genetic coefficients of variation showed an opposite trend to that for heritability: lint yield and boll-number values were large and lint percentage, micronaire value, and Pressley strength indices small. Expected responses to selection for the top 2·5 % of the population for lint yield and boll number at around 10% were usually higher than for other attributes.

Genotypic and phenotypic correlations were mostly similar but correlations often deviated widely between varieties. Positive lint yield correlations with micronaire value and negative lint yield correlations with Pressley strength index were recorded; these are often undesirable associations for breeding.

The association between the period of maintenance under Ord conditions and variability shown phenotypically in the original populations was not evident from the quantitative inheritance studies. Residual variability following breeding was considered as accounting for the larger portion of the genetic variability.

Response to selection primarily for lint yield among spaced plant populations of four American and one African variety of Gossypium hirsutum L., established in 1965—6 at Kimberley Research Station, was studied in three experiments conducted between 1966 and 1970.

In the first experiment, in which single-hill micro-plots of 3–5 plants per hill were used, the mean lint yield of progenies was larger than predicted from single plant heritabilities. In the second experiment, in which single-row plots were used, response to selection for lint yield was generally less than expected. In the third experiment, in which three-row plots were used, response to selection for lint yield was again less than expected and less than manifested in the second experiment. However, in all experiments responses to selection for lint percentage, lint quality properties, and height were close to expectations while some individual progenies substantially out-yielded their unselected parents.

The progressive decline in response to selection for lint yield from the first to thethird experiment, and the discrepancies between the actual responses and the expected responses for lint yield in all experiments, were interpreted mainly on a basis of intergenotypic competitive effects differing in sympathy with plot size and plant disposition.

It was concluded that the objective methods of selection practised were successful when judged on plant breeding criteria. It was also concluded that intra-varietal selection is an important technique by which genetic improvement can be achieved at regional breeding centres with limited resources.

Experiments were carried out to measure the components of canopy structure (on young spaced seedlings), their heritabilities and relationship to sward yield in the F1 generation of a diallel cross between six ryegrass populations.

Considerable differences existed between parent populations in both leaf length and tiller angle, but little difference existed in leaf angle. All the components of canopy structure were highly heritable, tiller angle, leaf length and leaf rigidity showing narrow sense heritabilities greater than 0·75.

There were large differences in yield between F1 families, moreover, when (a) Lolium perenne families, (6) L. multiflorum families and (c) L. perenne x L. mvltiflorum families were considered separately, leaf length and a composite character derived from leaf length and tiller angle (all measured on young spaced seedlings) were closely related to yield under sward conditions.

The plant breeding implications of these results are discussed.