THE VOLATILE PART OF PLANTS. 135 



stances, separation from which is difficult or imprac- 

 ticable. 



Chlorophyllan, obtained by Hoppe-Seyler from grass, 

 separates from its solution in hot alcohol in characteristic 

 acicular crystals which are brown to transmitted light, 

 and in reflected light are blackish green, with a velvety., 

 somewhat metallic lustre. This substance has the con- 

 sistence of beeswax, adheres firmly to glass, and at about 

 230 melts to a brilliant black liquid. The crystallized 

 chlorophyllan has a composition as follows : 



CHLOROPHYLLAN. 



Carbon 73.36 



Hydrogen 9.72 



Nitrogen 5.68 



Phosphorus 1.38 



Magnesium 0.34 



Oxygen 9.52 



100.00 



Chlorophyllan is chemically distinct from chlorophyl, 

 as proved by its optical properties, but in what the dif- 

 ference consists is not understood. Boiling alkali decom- 

 poses it with formation of chlorophyllanic acid that 

 may be obtained in blue-black crystals, and at the same 

 time glycerophosphoric acid and cholin, the decomposi- 

 tion-products of lecithin, are produced. Tschirch found 

 that chlorophyllan, by treatment with zinc oxide, yields 

 a substance whose optical properties lead to the belief 

 that it is identical with the chlorophyl that occurs in the 

 living plant. It was obtained as a dark-green powder, 

 but its exact chemical composition is not known. 



The special interest of chlorophyl lies in the fact that 

 it is to all appearance directly concerned in those con- 

 structive processes by which the plant composes starch 

 and other carbhydrates out of the mineral substances 

 which form its food. 



Xanthophyl is the yellow coloring matter of leaves 

 and of many flowers. It occurs, together with chlorophyl, 

 in green leaves, and after disappearance of chlorophy] 

 remains as the principal pigment of autumn foliage. 



