The Physiology of Flowering Plants - KHAM PHA MOI

GROWTH RATES 167Fig: 6:1 The effect oftemperature on growth(elongation) and respiration rate inthe bean Phaseolus coccineus,measured over a 2-hour period.At extreme temperatures, growthceases before respiration stops.From Bünning (1953). # Springer-Verlag GmbH & Co. KG.Light is not an absolute requirement for growth. Flowering plantsare normally dependent on light for photosynthesis and will starve in itsabsence, but they can grow in the dark if a supply of organic nutrient isavailable, and may be able to complete their life history in darkness.Maize has been grown from seed to seed-setting in the dark on anartificial sugar supply and Arisaema triphyllum ( Jack-in-the-pulpit, familyAraceae) has been raised in the dark from one large original corm forfour successive growth seasons. But light does profoundly affect growthand differentiation; it is indeed supremely important as a morphogeneticfactor, and plants grown in the dark are highly abnormal (Chapter10). Light actually suppresses elongation growth while promoting differentiation.In the field plants often grow more in height during thenight than during the day provided that the night temperature is not toolow. The growth of the date palm (Phoenix dactylifera)isstoppedcompletelyby direct sunlight. However, the controlling factor in the day/nightgrowth cycle may be water supply rather than light; this is the case withbamboos (Bambusa spp.) in various tropical regions which can grow intotal height about two to three times more during the night than duringthe day. Many studies indicate that growth is greater in the day iftemperature is the limiting factor and in the night if water is limiting.The highest growth rates often occur in the early morning (temperaturerising and water content still high) and early evening (temperaturestill high and water content increasing).6.6 Growth rates6.6.1 Comparing growth ratesQuantitative comparisons between the growth rates of living systemscan be made from two viewpoints. One can measure and compare