Pieces of the fronds of Enteromorpha linza, a green alga, growing just beneath the surface of the sea, of Porphyra umbilicalis, a red alga, of which the fronds of brownish-red colour which were growing on the side of a dock at half-tide level were selected, and of Delesseria sinuosa, a bright magenta-red alga from a depth of 18 metres in Passamaquoddy bay, were placed in vials of sea water (previously brought to pH 7 by the addition of KH2PO4), behind Corning red, green and blue filters, which had been brought to equal intensity in the photosynthetically active part of the spectrum, and exposed to sunshine. The gain in pH, due to the using up of CO2, was read at the end of 10 minute periods with a B.D.H. capillator set, and the photosynthetic rates for each species were determined by dividing the gain in pH (in hundredths of a unit) by the time. The photosynthetic rates of these three species in the different regions of the spectrum were very different, those of E. linza being red = 1.80; green = 0.16 and blue = 1.16, of P. umbilicalis red = 2.46; green and blue = 1.65, and of D. sinuosa red = 1.35; green = 1.25 and blue = 1.05. These data fit in very well with the transmission coefficients for red, green and blue light in the bay of Fundy at the place where the experiments were carried on, as green light penetrates best, blue next and red least.
Phototropin 1 and dim-blue light modulate the red light de-etiolation response