Effect of day and night temperatures during long photoperiods on the vegetative growth and flowering of Chrysanthemum morifolium Ramat

The influence of day and night temperatures in the range of 10–17°C on the vegetative growth under long days of 17 year-round cultivars of chrysanthemum was studied. The after-effect of the temperature regime on the time of flowering at 17°C under short days was also recorded.A decrease of the day or night temperature reduced growth, but the effect of the day temperature was much stronger than that of the night temperature. The temperature during the vegetative period had hardly any effect on the time of flowering at 17°C.The consequences for production and breeding are discussed.     

Vegetation changes in a moist grassland under altered water conditions

The vegetation of a small area of grassland in the southern part of the Netherlands was studied in 1965 and again in 1976. The grassland was subject to frequent flooding until 1970, when the water regime of the nearby river was altered. Phytosociological tables, vegetation maps and principal components ordinations were used to compare the vegetation in 1965 and 1976. In 1965 there was a clear gradient in vegetation from the lowest-lying eutrophic Phragmitetea communities, through the mesotrophic Molinietalia communities, to the oligotrophic Junco-Molinion communities furthest away from the river. This gradient was still recognisable in 1976 but was much less distinct. Indicator values of species are used to demonstrate the main ecological factors operative in the area. Changes in pattern and coarseness of the pattern on the vegetation maps are analysed, and the dynamics of the communities discussed.     

Runner formation on strawberry plants in autumn and winter

Summary In order to test strawberry selections for viruses, for which runners are necessary, the second writer tried, in connection with experiments carried out by Borthwick and Parker (1), to produce runners in the autumn and winter of 1952–53 by interrupting the dark period, however, without any result. Experiments carried out in 1953–54 have shown that too low a temperature was the cause of this failure, for runner formation in autumn and winter is dependent not only on day length but also on temperature.In the course of our 1953–54 experiments we found that in 1937 Darrow (2) had already made mention of the interrelation of temperature and day length in runner formation. However, it is not likely that sufficient runner formation would have taken place, had we applied his findings.     

Effects of temperature pre-treatments on the forcing of strawberry plants (cv. Glasa)

The results of an experiment, designed to study the effects of certain temperature treatments during the autumn season on the subsequent development of strawberries (cv. Glasa) during forcing, have been presented in this paper. This study was under-taken in the interest of both breeding new varieties suitable for forcing and improving the present forcing methods.Practical experience has shown that the chance of success is small when forcing is started before the 15th of January.In a recent publication it has been suggested to provide plants with strong artificial light for assimilation, which would make it possible to start forcing at an earlier date.In the present experiment, however, in which forcing was started as early as the 5th of January, good results were obtained under ordinary light conditions by previously exposing the plants to 12°C for three weeks in November. The pre-treated plants showed earlier flowring and fruiting, better fruit set and a higher yield than the control plants.These observations indicate that in order to obtain satisfactory results the inflorescences must have attained a certain stage of development at the beginning of forcing, and that this stage was reached at an earlier date by the accelerating effect of the temperature treatment.     

The selektron of the Institute for Horticultural Plant Breeding (IVT), Wageningen,the Netherlands

Summary A facility is described consisting of four growth rooms of 100 m² each in which temperatures and light intensities prevailing in glasshouses in winter in the Netherlands can be controlled.     

Introduction to an investigation into the possibilities of using physiological characters in breeding tomato for low energy conditions

Summary An introduction is given to a series of papers on an investigation into the possibilities of using physiological characters in breeding tomato for low energy conditions.     

Effects of temperature on growth and development of hybrid Tea-rose seedlings

Hybrid Tea-rose seedlings were grown, from germination to first flowering, at 6 constant temperatures between 10 and 26°C in greenhouses of our phytotron. All seedlings flowered regardless of temperature. When temperature increased, the juvenile period, the number of days to first flowering, the length of the leaved part of the shoot, the length of the flower stalk, the fresh weight of the shoot and of the root decreased; leaf number was not affected.     

Effect of the light intensity during flowering on stamen development in the strawberry cultivars ‘Karina’ and ‘Sivetta’

As in ‘Glasa’ (Smeets, 1976), a strong decrease in light intensity during flowering resulted in stamen abortion in early forced plants of ‘Sivetta’, but not in ‘Karina’. This has consequences for breeding.