1886. ] BOTANICAL GAZETTE, | 271 
1. A similarity of one or more chemical constituents is to be 
found in all plants which are equally developed, and on the same 
evolutionary plane. 
The evolution of chemical constituents in which they fol- 
low parallel lines with the evolutionary course of plant forms, the 
one being intimately connected with the other, and consequently 
that chemical constituents are indicative of the height of the 
scale of progression, and are essentially appropriate for a basis 
of botanical classification. In other words, that the theory of 
evolution in plant life is best illustrated by the chemical constit- 
_uents of vegetable form. 
e reasons offered in favor of a chemical basis of classifica- 
tion are: 
form are intimately associated with the origin and progression of 
plant life, and are consequently better adapted for classification 
than organs and tissues because as component parts less complex. 
the invariable composition and structure of given de- 
terminate chemical constituents. 
4. The percentage of any given compound in a plant would 
gauge the progression or retrogression of a plant, species 0 
genus, and would accentuate the characters of progression, adap- 
tion, and filiation. 
Variations in chemical constituents would be detected by 
analysis earlier than consequent variations of organs or tissues. 
t is a law of internal influences controlling function and 
modifying forms rather than of external forces, hence a study o 
the elements of the innermost structure of plant life is a study 
of that law and of life itself. ; 
All chemical constituents will not answer as means of classi- 
t. . . 
The chemical study of plants is meant to include micro- 
chemistry in its application to histology and physiology, in de- 
