METABOLIC PROCESSES IN THE PLANT. 341 



a red rose or peony are macerated with a little water in a mortar, 

 the solution obtained on filtering is red in colour, and according to 

 my observations (I experimented with Paeonia) becomes blue on 

 addition of ammonia. Addition of Hydrochloric acid restores the 

 red colour of the fluid. It may also be of interest to examine 

 the extracts from yellow or red] flowers spectroscopically. 2 For 

 this purpose the methods given in 7 are to be employed. 



It is also instructive to observe the pigments contained in the 

 heart- wood of many trees. We examine, for example, a transverse 

 section of red sandal wood (the wood of Pterocarpus santalinus). 



FIG. 115. From the upper side of the calyx of Tropaeolum majus. Lower wall of an 

 epidermal cell with the adjacent chromatophores. Magn. 5W. (After Sjtrasburger.) 



The wide vessels rest against the bands of wood parenchyma, 

 which run parallel with the annual rings. We further see the 

 numerous medullary rays, whose cells contain a resinous dark 

 red mass, and the wood fibres with strongly thickened walls. All 

 the elements of the wood have pigments in their membranes 

 consisting specially of the red Santalic acid. Distilled water 

 only extracts traces of pigment from sandal wood, but with 

 ummonia we easily obtain a carmine red extract. 



The elements of Brazil wood (Cresalpinia echinata) hold in their 

 membranes a yellowish pigment, brasilin. If we treat Brazil 

 wood with hot water, a fair amount of this pigment goes into 

 solution, and the fluid takes on a blood-red coloration on addition 

 of ammonia or potash. 3 



