274 PLANT AND ORGANIC CHEMISTRY 
containing oils, and since, in many genera in which this sub¬ 
stance has been found, certain fixed or ethereal oils also occur, 
it may be inferred that this constancy relates to their chemical 
evolution. The palms are the lowest plants which contain cou- 
marin; then it occurs in the grass and rose families on the same 
evolutionary plane, also among the leguminous, madder, rue, 
and portulaca orders, and in orchids and Composite. These 
plants are characterized by their aromatic and volatile oily pro¬ 
ducts; and vanillin, the fragrant principle of vanilla, also oc¬ 
curs among orchids. It may be noted that oils are formed abun¬ 
dantly in the highest plants. 
A knowledge of the chemical compounds, as they are found 
grouped in plants, is a first step towards the study of their 
evolution, and acquaintance with the conditions which control 
their synthesis and gradual formation in the plant can only be 
had by patient research. The simpler compounds of which any 
complex substance is built, if located as compounds of lower 
plants, would indicate the lines of progression from the lower 
to the higher groups. 
It has been already said that every plant contains compounds 
peculiar to it, but certain compounds seem to play a special 
part in plant evolution, since the wax and tannin of the vascu¬ 
lar cryptogams lead to the tannin and wax groups of the apet- 
alous plants, and the starch of these lower plants to the great 
starch groups of the monocotyledonous. It will not be out of 
place to note here that the greatest accumulations of starch oc¬ 
cur in plant orders just before they pass on to a higher plane of 
evolution. This is seen, for example, in the palm and neigh¬ 
boring orders of the first plane, and among the Lirioideae of the 
second plane, since these plants are the richest in starch con¬ 
stituents, and it seems as if they were preparing by large reserve 
of food-supply for their higher position, represented by more 
evolved groups, where the demands for nutrition are greater. 
Again, the fine of cane sugar indicates that sugar occurs promi¬ 
nently in plants passing from simplicity to multiplicity of floral 
elements, and the glucosides in their turn are found in the mid¬ 
dle stage of plant development, assisting the plants to the high¬ 
est plane of cephalization. 
