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Abstract
Net photosynthesis, as measured by dry matter changes, was reduced following the dark periods when foliage plants were grown in extended, alternate dark-light cycles. Longer dark periods resulted in greater reduction; however, recovery was observed if the light duration was increased. No visual quality reduction was observed in Tradescantia fluminensis Veil and Asparagus setaceus Jessop which was grown under 14 days light: 14 days dark cycles for 84 days. Similarly, the quality of mature leaves and stems of Philodendron scandens Subsp. oxycardium (Schott) Bunt grown under 24 days dark: 24 days light cycles for 96 days was not impaired; however, new shoots and leaves were abnormal. Dry matter partitioning of Philodendron was affected by light conditions and growth activity. In plants with no active growth, the dry weight of leaves, stems, and roots was increased under adequate light condition and decreased under darkness. Stems were stronger sinks than leaves. In all treatments, when new shoots started their active growth, they became the main carbohydrate sinks with a concomitant reduction of weight of the mature organs. Reduction in percent dry matter following the lowering of the light intensity was observed. Determining and measuring the critical percent dry matter at which plant injury occurs are suggested as practical methods to evaluate the plant’s condition and how it may respond during and after the marketing period.