Light saturation of the individual bottom leaf occurred at an irradiance of approximately 230 J m-2 s-1 PAR and for the second leaf at 180 J m-2 s-1. The light-response-curve for the individual leaf showed a distinctly asymptotic curve with a maximum rate of net photosynthesis attained at 1/4 to 1/3 of full sunlight. These photosynthesis-light-response curves
agree very well with crops classified as Ca-species (Trenbath and Angus, 1975). Taking into consideration the low net photosynthesis rate at high global radiation (Figs. 1 and 2) and the temperature range 10--20 ° C (Fig. 3),
it appears that Tulipa sp. cultivar 'Apeldoorn' can be classified as a Caspecies. Willmer and Dittrich (1974), looking at ~4CO2 -fixation by epidermal tissue of an unspecified tulip cultivar, concluded that the CO2 -fixation pattern
of the labelled products was, indeed, typical of Ca -species.