Apr. 1896.] BOTANICAL SOCIETY OF EDINBURGH. 



547 



CLASSIFICATION OF THE CHROMOGENS WHICH ARE OF 

 GLUCOSIDE NATURE. 



Usually remain 

 in ]ilant in 

 condition of 

 elironiOKens. 



2. Give rise to pig- 

 ments within 

 the plant. 



a. Tannins of young shoots, _ ,-_ ^^^^^^^ 



of young tloral leaves, ti:, | •'^^jj, 



of unripe fruits, etc. '^ ■- 



pigments 



h. Tannins (?) of wood. 

 c. Tannins of liark. 



c [~= Hematoxylin, 



Brasilin. etc. 



$ r 



Pliloljaphenes. 



Of the other plant pigments not yet mentioned, chloro- 

 phyll and etiolin are, of course, by far the most important. 

 From the present point of view, however, there is little to 

 say of either, for, in spite of numerous investigations, little 

 is known of their constitution or origin. The two are 

 probably very nearly allied in composition, and differ from 

 most other plant pigments in containing nitrogen. That 

 many plants, when grown in normal conditions, contain 

 chlorophyll, is at present an observed fact beyond which it 

 is impossible to go. 



We have already seen that, normally, chlorophyll seems 

 to be always associated with lipochromes, and this is pro- 

 bably also true of etiolin. The lipochromes are not, how- 

 ever, the only pigments thus associated ; many cryptogams 

 have their chlorophyll masked by other well-defined colour- 

 ing-matters. Thus the Eed Algic owe their apparent 

 colour to a reddish pigment which is soluble in water, 

 forming a fluorescent solution, and which, according to 

 Krukenberg, resembles very closely a red pigment found in 

 some sponges. Its presence in the Floridere appears to be 



