The botanical classifications based upon morphology are so frequently
unsatisfactory, that efforts in some directions have been made to
introduce other methods.[48]
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 leguminosae 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
_Haematoxylon_ and _Saraca indica_.
The discovery[49] of haematoxylin in the _Saraca indica_ illustrates
very well how this plant in its chemical, as well as botanical,
character is related to the _Haematoxylon 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 leguminosae. The
leguminosae 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.
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