242 LECTURE XII. 



colouring-matters (in rare cases also the blue), the latter with the white, 

 violet, blue,' and red (rarely the yellow). According to the researches 

 of Weiss, in particular, the fixed colouring-matters are derivatives of 

 chlorophyll; the corpuscles in which they are present are first of all 

 green, and gradually change colour as the flower opens, or as the fruit 

 ripens. The best-known of these is anthoxanthin, the colouring-matter 

 of yellow flowers. The dissolved colouring-matters are, in white flowers, 

 antholeucin, in blue anthocyanin. The violet red and violet colours are 

 probably due to the presence of acids or acid salts in the cell-sap which 

 act upon the anthocyanin. In some instances colouring-matters are 

 present in both these forms, for instance, yellow corpuscles in a cell with 

 a red, blue, or violet cell-sap : in certain leaves, those of the Copper-Beech, 

 the Copper-Hazel, etc., the cells contain chlorophyll-corpuscles and 

 purple cell-sap. It is probable that the dissolved colouring-matters are 

 derived from tannin or other glucosides. 



Among the Thallophytes, chlorophyll is always present in the Algae, 

 and it is always absent in the Fungi. Many of the Algae are, however, 

 not of a green colour. For instance, the Phycochromaceae or Cyano- 

 phyceae, are bluish-green, this colour being due to the presence of a 

 blue colouring matter, phycocyanin^ in addition to chlorophyll : again the 

 Diatomaceae and the Fucoideas are yellow or brown ; this is due to the 

 presence of a brown colouring-matter, phycoxanthin, which masks the 

 green colour of the chlorophyll which is present : finally, the red Seaweeds 

 or Florideae contain, in addition to chlorophyll, a red colouring-matter 

 tetmz&phycoerythrin. Phycocyanin and phycoerythrin are both soluble 

 in water. 



Although the Fungi do not contain chlorophyll, yet other colouring- 

 matters are frequently present in them. These occur in all Fungi, from 

 the Bacteria to the Agarics, and they are of different hues, yellow, green, 

 red, brown, and blue. The Lichens are especially rich in these sub- 

 stances : the Algas which from part of their structure (gonidia) contain of 

 course chlorophyll, but the Fungus-part of the Lichen often contains 

 other colouring-matters in quantity. The Lichens which are used for 

 the commercial preparation of certain pigments, such as Litmus (blue), 

 do not contain these substances as such, but colourless bodies, such as 

 erythrin, lecanorin, etc., which, on decomposition give rise to substance 

 orcin (a dihydroxyl derivative of toluene), and it is from this that the 

 pigments are obtained by various processes. 



With regard to their chemical nature, the colouring- 

 matters of plants are considered to be closely connected with 

 the aromatic group of substances. As to their physiological 

 significance, they may be regarded simply as waste-products 

 in so far as their direct use in constructive metabolism is 



