1887] Comparative Chemistry of Higher and Lower Plants, 721 
absorbing questions of the moment for investigation, but the 
evolution of compounds from these elements and their possible 
influence upon the external forms of plants is of equal interest. 
That directive force which controls the different groupings of 
atoms in a molecule under the solid, liquid, or gaseous forms of 
matter, manifests itself in still more complicated conditions in 
each grade of the chemical compounds of living cells, and thus 
from the single cell to the highest of plants is ever active. 
- It is not my wish to claim for plant chemistry more than the 
facts at my disposal will allow; though in the past, and this 
should not be overlooked, without the aid of the imagination to 
penetrate the avenues of the unknown, many of our well-estab- 
lished scientific facts would still be buried from sight. 
The chemical analysis of the dead plant and the study of the 
chemical changes occurring in the living plant are among our 
means for some of these investigations; and much of all the 
knowledge derived from each field of chemical research may be 
utilized in aiding to unravel the mystery of these changes in the 
vegetable cell. 
in the mineral kingdom certain elements are invariably asso- 
ciated with others, as nickel with cobalt; and in plants we find 
not only two or more compounds invariably present together,— 
îe., tannin and starch in the tannin groups, lime and saponin in 
the pink family, Caryophyllacez,’ resins and saponin in all of 
the saponin-containing groups, and sugar and silica in the 
grasses, Gramineze,—but also in certain plant groups we notice 
the predominance of special compounds, and their absence in 
other groups. The grouping of these compounds in definite 
association must bear some relation to their respective sequence 
and formation, and cannot be the result of accident. That the 
; finchona plant does not manufacture the alkaloids of the poppy, | 
t each its own particular series of compounds, illustrates this. ` 
I have said, elsewhere, “ the chemical compounds of plants 
do not occur at random. Each stage of growth and develop- 
_ Ment has its own particular chemistry. . . . The result of ex- 
_ Periment shows that the presence of certain compounds is es- 
-sential to the vigor and development of all plants, and particular ` 
r ži Die Pfanzenstoffe, by Hilger and Husemann, p. 532; E. v. Wolff, J. pr- Chem., 
A. 24; lii. 86; Wolf, Panien a 1881, 144, 145- 
? *The Chemical Basis of Plant Fi 
_ TOL XX1—No, 8. ee 
