Under the Schizomycetes to which the Micrococcus and Bacterium[10] belong are found minute organisms differing much in form and in the coloring[11] matters they produce, as that causing the red color of mouldy bread.

The class of lichens[12] contains a number of different coloring substances, whose chemical composition has been examined.  These substances are found separately in individuals differing in form.  In the Polyporus[13] an acid has been found peculiar to it, as in many plants special compounds are found.  In the agariceae the different kinds of vellum distinguish between species, and the color of the conidia is also of differential importance.  In all cases of distinct characteristic habits of reproduction and form, one or more different chemical compounds is found.

In the next group of the musiceae, or mosses, is an absence of some chemical compounds that were characteristic of the classes just described.  Many of the albuminous substances are present.  Starch[14] is found often in large quantities, and also oily fats, which are contained in the oil bodies of the liverworts; wax,[15] organic acids, including aconitic acid, and tannin, which is found for the first time at this evolutionary stage of the plant kingdom.

The vascular cryptogams are especially characterized by their mineral composition.[16] The ash is extraordinarily rich in silicic acid and alumina.

Equisetum[17]..........silicic acid     60 per cent. 
Aspidium...............  "     "        13
Asplenium..............  "     "        35
Osmunda................  "     "        53
Lycopodium[18].........  "     "        14
"         ........ alumina   26 to 27
"         ........ manganese 2 to 2.5

These various plants contain acids and compounds peculiar to themselves.

As we ascend in the plant scale, we reach the phanerogams.  These plants are characterized by the production of true seeds, and many chemical compounds not found in lower plants.

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.