THE PHYSIOLOGY OF COLOR IN PLANTS.
served by many of the coloring substances besides chlorophyll are by no means secondary in distribution or importance to the individual plant to the exterior adaptations described above.
The principal coloring matters among the higher plants besides chlorophyll (leaf-green) are those which have been grouped under the terms erythrophyll, xanthophyll, and anthocyan. Of these substances the chemical and physical properties of chlorophyll are best known, although its exact composition is yet undetermined. Not only is our chemical knowledge of the non-green colors very vague, but it is thought that a great number of different substances are grouped under each of the above and other color terms. Thus, for instance, anthocyan is made to include the large number of substances to which are due the red, blue, violet,
Fig. 1.—I. Spectrum of Chlorophyll showing Seven Absorption Bands. The two in the red-yellow between B and D, and the three in the blue-violet, beyond F, are the most important and characteristic. The bands between D and E are most marked in the spectra of solutions which have been exposed to the air and light some time, and are believed to be due to disintegration products of chlorophyll.
II. Spectrum of Amaranth-red. All the rays except those falling between B and D have been absorbed.
III. Spectrum of Autumnal Color of Leaves of Ampelopsis. All the rays except a part of those falling between C and D have been absorbed.
and purple colors of such plants as the violet, beet, canna, rose and amaranth. Only so much is known of the formation of these color substances as to justify the assertion that many of them are produced as disintegration products of the glucosides and others from a mother substance—chromogen.
The coloring matters of plants may be in solution in the cell sap as in the beet and amaranth, in irregular solid masses in the sap or protoplasm, as in nasturtium (Tropœolum); or may be incorporated in the cell wall, as in logwood (Hæmatoxylon); or