Note 47 — Chapter III · DIFFERENTIATIONS AMONG THE OUTER TISSUES OF PLANTS.

The current doctrine that chlorophyll is the special substance concerned in vegetal assimilation, either as an agent or as an incidental product, must be taken with considerable qualification. Besides the fact that among the Algæ there are many red and brown kinds which thrive; and besides the fact that among the lower Archegoniates there are species which are purple or chocolate-coloured; there is the fact that Phænogams are not all green. We have the Copper-Beech, we have the black-purple Coleus Verschaffeltii, and we have the red variety of Cabbage, which seems to flourish as well as the other varieties. Chlorophyll, then, must be regarded simply as the most general of the colouring matters found in those parts of plants in which assimilation is being effected by the agency of light. Though it is always present along with the red and brown pigments, yet there is much evidence to show that these are the actual assimilative pigments.