SEASONAL CHANGES IN NET ASSIMILATION AND LEAF GROWTH OF YOUNG TOMATO PLANTS
Watson (1952) has pointed out that "since net assimilation rate depends on both photosynthesis and respiration, there can be no ideal basis of reference for net assimilation that will render net assimilation rate wholly independent of internal factors. The best course seems to be to use a basis of reference appropriate for photosynthesis, since this must be the dominant process whenever increase in dry weight is taking place…… Instead of attempting to devise a basis of reference for net assimilation rate that conforms more closely to the ideal, it is better to continue to use the leaf area basis for the sake of uniformity…… net assimilation rate and total leaf area may be regarded as measures of the efficiency and of the capacity of the photosynthetic system".
Seed of the "Potella" variety of glasshouse tomato was sown at weekly intervals throughout the year beginning on 23rd November, 1962. Within a few days of germination, twenty seedlings were pricked off into John Innnes Potting Compost No. 1. in parallel sided 4 ¼" diameter, 3 ½" tall, plastic pots. The pots were placed on a capillary bench to minimise variability due to variation in water supply. To improve the uniformity of the rooting medium, the loam required for all sowings was shredded and mixed at the beginning of the experiment, and the potting for each sowing was prepared from this source of loam at weekly intervals. The glasshouse