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The 77 K fluorescence spectra during the development of dark-grown primary needles. Excitation wavelength: 440 nm. The spectra were normalized to their fluorescence emission maximum. A, P. jeffreyi. Curve a, 3 weeks old; curve b, 4 weeks old; curve c, 5 weeks old. B, P. sylvestris. Curve a, 5 weeks old; curve b, 6 weeks old; curve c, 7 weeks old.
