It will be convenient in speaking of these higher groups to follow M. Heckel's[19] scheme of plant evolution. All these plants are grouped under three main divisions: apetalous, monocotyledonous, and dicotyledonous; and these main divisions are further subdivided.
It will be observed that these three main parallel columns are divided into three general horizontal planes.
On plane 1 are all plants of simplicity of floral elements, or parts; for example, the black walnut, with the simple flower contained in a catkin.
On plane 2 plants which have a multiplicity of floral elements, as the many petals and stamens of the rose; and finally, the higher plants, the orchids among the monocotyledons and the composite among the dicotyledonous plants, come under the third division of condensation of floral elements.
It will be impossible to take up in order for chemical consideration all these groups, and I shall restrict myself to pointing out the occurrence of certain constituents.
I desire now to call attention to chemical groups under the apetalous plants having simplicity of floral elements.
Cassuarina equisetifolia[20] possibly contains tannin, since it is used for curing hides. The bark contains a dye. It is said to resemble Equisetum[21] in appearance, and in this latter plant a yellow dye is found.
The Myrica[22] contains ethereal oil, wax, resin, balsam, in all parts of the plant. The root contains in addition fats, tannin, and starch, also myricinic acid.
In the willow and poplar,[23] a crystalline, bitter substance, salicin or populin, is found. This may be considered as the first appearance of a real glucoside, if tannin be excluded from the list.
The oak, walnut, beech, alder, and birch contain tannin in large quantities; in the case of the oak, ten to twelve per cent. Oak galls yield as much as seventy per cent.[24] The numerous genera of pine and fir trees are remarkable for ethereal oil, resin, and camphor.