CHEMICAL CONSTITUENTS OF PLANTS 169 
passing from their lower to their higher stages. Saponin is 
invariably absent where the floral elements are simple; it is 
invariably absent where the floral elements are condensed to 
their greatest extent. Its position is plainly that of a factor 
in the great middle realm of plant life when the elements of 
the individual are striving to condense and thus increase their 
physiological action and the economy of parts. All the great 
groups that contain saponin are closely allied and possess 
other properties in common, as fibrous or bulbous roots, root¬ 
stocks, tubular character of some part of the flower, and a 
climbing tendency in Smilaceoz and some of the Sapotacecz. 
Numerous analogous examples of a correspondence between 
morphology and chemical constituents were advanced, and 
the following conclusions reached: 
1. A similarity of one or more chemical constituents is to 
be found in all plants that are equally developed, and on the 
same evolutionary plane. 
2. The evolution of chemical constituents in which they 
follow parallel lines with the evolutionary course of plant forms, 
the one being intimately connected with the other, and con¬ 
sequently that chemical constituents are indicative of the 
height of the scale of progression, and are essentially appro¬ 
priate for a basis of botanical classification. In other words, 
that the theory of evolution in plant life is best illustrated 
by the chemical constituents of vegetable form. 
The reasons offered in favor of a chemical basis of classi¬ 
fication are: — 
1. The disagreement among botanists themselves, depend¬ 
ing upon the insufficiency of the present methods of classifica¬ 
tion. 
2. Chemical constituents, or the constructive elements of 
form are intimately associated with the origin and progres¬ 
sion of plant life, and are consequently better adapted for 
classification than organs and tissues, because, as component 
parts, less complex. 
3. By the invariable composition and structure of given de¬ 
terminate chemical constituents. 
4. The percentage of any given compound in a plant would 
