There has been comparatively little study of the chemical principles of plants from a purely botanical view. It promises to become a new field of research.
The leguminosæ are conspicuous as furnishing us with important dyes, e.g., indigo, logwood, catechin. The former is obtained principally from different species of the genus Indigofera, and logwood from the Hæmatoxylon and Saraca indica.
The discovery[49] of hæmatoxylin in the Saraca indica illustrates very well how this plant in its chemical, as well as botanical, character is related to the Hæmatoxylon campechianum; also, I found a substance like catechin in the Saraca. This compound is found in the acacias, to which class Saraca is related by its chemical position, as well as botanically. Saponin is found in both of these plants, as well as in many other plants of the leguminosæ. The leguminosæ come under the middle plane or multiplicity of floral elements, and the presence of saponin in these plants was to be expected.
From many of the facts above stated, it may be inferred that the chemical compounds of plants do not occur at random. Each stage of growth and development has its own particular chemistry.
It is said that many of the constituents found in plants are the result of destructive metabolism, and are of no further use in the plant's economy. This subject is by no means settled, and even should we be forced to accept that ground, it is a significant fact that certain cells, tissues, or organs peculiar to a plant secrete or excrete chemical compounds peculiar to them, which are to be found in one family, or in species closely allied to it.
It is a fact that the chemical compounds are there, no matter why or whence they came. They will serve our purposes of study and classification.
The result of experiment shows that the presence of certain compounds is essential to the vigor and development of all plants and particular compounds to the development of certain plants. Plant chemistry and morphology are related. Future investigations will demonstrate this relation.
In general terms, we may say that amides and carbohydrates are utilized in the manufacture of proteids. Organic acids cause a turgescence of cells. Glucosides may be a form of reserve food material.
Resins and waxes may serve only as protection to the surfaces of plants; coloring matters, as screens to shut off or admit certain of the sun's rays; but we are still far from penetrating the mystery of life.
A simple plant does what animals more highly endowed cannot do. From simplest substances they manufacture the most complex. We owe our existence to plants, as they do theirs to the air and soil.