UNORGANIZED CELL-CONTENTS. 
25 
tion, quite a number of principles give a green color 
with various other reagents, as emetine with sulphuric 
acid, gelsemin with nitric acid, and the cinchona alka- 
loids with chlorine water and ammonia. 
(6) Yellow coloring principles include a number of 
substances which occur in a crystalline condition, as 
chelidoxanthin from Chelidonium majus, quercitrin from 
Quercus tinctoria. A large number of volatile and fixed 
oils have a yellow color, which may he due to xantho- 
phyl, or some modification of cblorophyl, as etiolin. 
(c) Red coloring principles include some of the most 
important coloring substances of the arts, as crocin, 
alizarin, purpurin, morindin, haematoxylon, alkanna 
red, etc. The various tannins and tannoids yield upon 
oxidation red-coloring principles, and many of the 
alkaloids and other active principles produce red-col- 
ored compounds with various reagents. 
(d) The blue or purple coloring principles, like the green, 
are limited in number, and are usually more or less 
difficultly soluble in water. They include some of the 
principal commercial dyes, as indigo blue. A number 
of the volatile oils of flowers have a blue color, as of 
Matricaria chamomilla and Achillea millefolium, this no 
doubt being due to the solvent action of the oil on the 
coloring principle of the flower. 
7. CALCIUM OXALATE. 
Calcium oxalate is found in many of the higher 
plants, and in the algae and fungi as well; while in the 
mosses, ferns, grasses and sedges it is seldom found. 
It occurs in plants in crystals of either the monoclinic 
or tetragonal system. The crystals dissolve in any of 
the mineral acids without effervescence and are 
usually detected with dilute hydrochloric acid. The 
crystals of the monoclinic system are rather widely 
