SUMMARY This paper reports the results of experiments carried out in Surrey and Cardiganshire (lat. 51o 19′ N. and 52o 25′ N.) and a t Werribee in Victoria (lat. 37o 54′ S.) designed to test some Australian and British wheats grown under various periods of illumination. Light of weak intensity (4–5 c.P.) was employed to prolong the daily period.2. Generally the Australian varieties were “earlier” at all centers under all periods of light than the British. A sharp distinction between the reaction of spring and winter varieties was observed under short periods of light. Retardation or omission of floral development was always accompanied by prolonged vegetative vigour. The influence of such treatments upon the longevity of the plants was observed. Observations are made upon the relationship of the photoperiodic response to the geographic source of varieties. The results are very briefly considered from the standpoint of the C/N hypothesis and the utilisation of the products of photosynthesis. Certain economic aspects of the work are indicated.

Since the year 1927, observations have been made in Victoria on the development of wheat crops of various varieties grown in four different districts of the State.The method used was based on that employed by Engledow in his “Investigations on Yield in Cereals,” by taking counts on numbers of plants in various “foot length” samples scattered in a systematic manner over the areas studied.The basis of the observations was the determination of the values which comprise yield, viz. p = numbers of plants, e = ears per plant, n = number of grains per ear, g = average weight of grain.

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