: 804 Comparative Chemistry of Higher and Lower Plants, 
the preceding stages of chemical evolution are represented 
_ loids are found in the monimia, hemp, laurel, and ama 
3 j. grass, is one illustration ; its occurrence is limited to those 
: Containing oils, and, since in many genera in which this su 
___ has been found certain fixed or ethereal oils also occut, it 
__ be inferred that this constancy relates to their chemical evo! 
> : en palms are the lowest plants which contain coumarin 
NON in the grass and rose families on the same evolu 
ae Sat po among the leguminous, madder, rue, pe pe 
8 and in orchids and ita, ar 
acterized Composit, These plants ar 
_ orchids. It may be noted that oils are formed abundantly 
-bichet ol 
. o A knowledge of the chemical compounds, as they arè 
-and the strychnos orders, and to the organic acids of the valerian 
_ order, and the aromatic and volatile compounds of the 
are found in many orders. 
‘a 
as well as resins, in other saponin orders. Saponin may 
called a constructive element in developing the plant from 
multiplicity of floral element to cephalization of these organs, 
` Among the members of the higher groups of plants many 
a certain point, when the plants acquire other chemical ch 
teristics,—7.2., indigo, hzmatoxylin, and other coloring-m: 
of the leguminous groups, and the dyes of the madder 
give way to the alkaloids of the cinchona, the coffee, the atropa, 
, 
posite. 
Alkaloids, though so widely distributed, are not found inth 
very lowest nor the highest plants. Their occurrence in 
has been already noted. In flowering plants among the | 
apetals, piperin, the alkaloid of Piperaceæ, occurs; also, 
orders, and in colchicum; but they are exceptional in 
lower groups, and belong properly to dicotyledons, where 
Besides the occurrence of compounds peculiar to distil 
plants or whole plant groups, another class is found, and t 
substances of this class may be scattered quite generally thr 
the plant kingdom, but always associated with some other í 
pound. pea 
-~ Coumarin, the odorous principle of tonka-bean and ven 
. or their aromatic and volatile oily products; 
fragrant principle of vanilla, also occurs 
highest 
Grouped in plants, is a first step towards the study of 
