Formative Effects of Environmental Factors as Exemplified in the Development of the Onion Plant

Abstract

DURING the last two decades, discoveries of great importance have been made in the field of plant morphogenesis, and the predominant part played by the external factors of day-length and temperature has been established. Applications of this knowledge to the control of plant growth in agricultural and horticultural practice have led to important results, for example, in the forcing of bulbs (Blaauw, Van Slogteren and their associates^1,2) and the development of vernalization as a practical technique in the U.S.S.R.^3,4,5. In both these cases temperature effects are concerned; with regard to the length of day effects ('photoperiodism') the ample empirical knowledge we owe to Garner and Allard and subsequent investigators⁶ has so far yielded fewer practical results than might have been anticipated. The work dealt with in this article has brought to a focus these lines of research in an attempt to elucidate the behaviour of the onion plant.