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 x 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 line 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. 



