24 
PLANT MORPHOLOGY. 
While the microchemical study of the alkaloids 
requires considerable technic, still, in certain drugs, 
their detection is quite simple, as in nux vomica, stro- 
phanthus and hydrastis. 
4. THE GLUCOSIDES. 
The glucosides, like the alkaloids, are also probably 
formed in the protoplasm. They are compounds of 
glucose and other principles and may be classed among 
the reserve products. In some instances they readily 
separate in the plant cell, as hesperidin ; while others 
give characteristic color-reactions, as crocin, salicin 
and coniferin, but in most instances they are either 
decomposed or the compounds which they form have 
no distinct microchemical value. 
5. THE GLUCO-ALKALOIDS. 
Gluco-alkaloids represent a class of compounds inter- 
mediatebetween thealkaloids and glucosides, possessing 
characteristics of each. To this class belongs achillein, 
found in various species of Achillea and probably 
solanin, found in a number of species of Solanum. 
6. COLORING PRINCIPLES. 
Coloring principles other than those associated with 
plastids occur dissolved in the cell sap or in ethereal 
oils, or are impregnated in or incrusted upon the cell 
w r all. These principles may be divided according to 
the colors they naturally possess or acquire upon treat- 
ment with reagents, into the following groups : 
(a) Green coloring principles as such are limited in 
number and include substances like digitoleic acid. 
Many of the essential oils are green in color, this being 
due probably to dissolved chlorophyl. A number of 
tannin principles acquire a green color with iron salts, 
as those of cinchona, quercus and krameria. In addi- 
