Research and observations on how climate effects the growth and yield of the tea plant are reviewed. Despite differences in the types of tea grown and the cultural techniques practiced in the different tea areas, an attempt is made to define quantitatively the climatic conditions needed to maintain growth rates at a high level. The need for critical work in the future is emphasized.

High yield in the tapioca varieties studied appears to be associated with sink activity of the tubers and consequently with crop index. Growth measurements indicate that assimilation is significantly affected by sink activity as well as by the functioning of the assimilation apparatus. The form of the crop growth curve, and the effect of spacing on yield and distribution of dry matter are also considered.

Results from an experiment with maize (variety NEH 1151) at three plant densities indicated that normally favourable environmental conditions promoted tillering and it was difficult to maintain the desired tiller densities. The higher densities produced more vegetative dry matter but less grain than the lower densities. In a second experiment, where tillers were removed from the plants, there was no advantage because the remaining tillers grew larger to compensate for the removal. It is concluded that it is desirable to breed or select for non-tillering varieties where other management parameters can be controlled.

Yield response to a range of plant densities (0·7–7·2 plants m.−2) achieved by uprooting plants at random was curvilinear, with an optimum plant density of 3·3 plants m.−2 at which fertilizer increased the yield at Makoka by over 1000 kg. ha.−1 to 2227 kg. ha.−1. There was no interaction between fertilizer and plant density. At Ngabu there was no response to fertilizer. Top dressing was effective on unfertilized cotton at Makoka, but filling in was ineffective at both sites. A method of partitioning components of yield is described which illustrates the stages of plant development which benefitted or were adversely affected by the different agronomic practices.

Experiments on seed rate, time of weeding and thinning confirmed that lower seed rates, weeded and thinned early, give higher yields. A reduction in yield of 400 kg.ha.−1 seed cotton caused by late weeding emphasized that farmers who spray should limit their acreage to that which can be weeded satisfactorily.

The extent of natural cross-fertilization in sesame was studied in two varieties, with contrasting flower colour, planted at two locations; in alternate rows or alternate holes; in adjacent or non-contiguous plots; and at 6 different spacings. The average out-crossing for the different treatments ranged between 3.1 and 6.7 per cent. The non-contiguous plots showed a higher degree of out-crossing than adjacent plots, in which there was a decrease in the extent of cross-pollination with increase in the distance between the dominant and the recessive parents. Alternate holes gave a higher percentage than alternate rows.

A three-year study on the development of oil, protein and dry matter in sesame seeds showed that oil percentage increased rapidly 11–17 days after fertilization, reaching a maximum in 20–23 days. There was no change in the iodine value of the oil after 18 days from fertilization. Accumulation of protein was more gradual, but there was no appreciable increase after the ‘seeds’ were 27 days old. Dry matter increased more slowly than either oil or protein and there was little increase after the ‘seeds’ were 34 days old. The implications of these findings on problems of harvesting the crop are discussed.

The effect on cross pollination of four directions and six distances from the marker variety in Egyptian cotton was investigated. The percentage of cross pollination did not differ appreciably in the different directions but there were significant differences in cross fertilization among the six distances. A linear relation was observed between cross pollination per cent and distance up to 8.8 m. from the marker variety. Implications of these findings on various aspects of cotton breeding methodology are discussed.

Effects of Gamma BHC in controlling capsids on cocoa in a large-scale experiment have been assessed at 10 and 12 sites, over seven seasons, in the Eastern and Ashanti regions of Ghana. The treatments effect was not significant for the whole Eastern region, whereas it was for the Ashanti region except in the first season. For the Ashanti region the overall treatment and seasons effects were very highly significant, whereas their interaction was not. There was an increase in response with time, though the rate of response was decreasing with time.

Artificial defoliation was used to simulate grazing by cutting-grass or cane-rat (Thryonomys swinderianus), on three rices with durations of 110–115, 130–135 and 140–145 days respectively, defoliated before, during and soon after tillering by removing leaves to half, two-thirds and the total height of the plants. All varieties showed marked compensatory growth, resulting in increased tillering and yield, especially when defoliated during tillering, but yield fell when foliage was removed after tillering, especially with shorter duration rice. Defoliation to half the height of the plant during tillering had the most beneficial effect, whereas removal of all leaves to soil level after the tillering stage had the most adverse effect.