This difference in the physical character and chemical reaction of these fixed oils may be due to the presence of free fatty acid and glycerides in varying proportions in the four parts of the plants. It is of interest to note that, in the subterranean part of the Yucca, the oil extracted from the bark is solid at the ordinary temperature; from the wood it was of a less solid consistency; while the yellow base of the leaf contained an oil quite soft, and in the green leaf the oil is almost fluid.
Two new resins were extracted from the yellow and green parts of the leaf. It was proposed to name them yuccal and pyrophæal An examination of the contents of each extract showed a different quantitative and qualitative result.
Saponin was found in all parts of the plant.
Many of the above facts have been collected from the investigations of others. I have introduced these statements, selected from a mass of material, as evidences in favor of the view stated at the beginning of this paper.[41] My own study has been directed toward the discovery of saponin in those plants where it was presumably to be found. The practical use of this theory in plant analysis will lead the chemists at once to a search for those compounds which morphology shows are probably present.
I have discovered saponin in all parts of the Yucca angustifolia, in the Y. filimentosa and Y. gloriosa, in several species of agavæ, and in plants belonging to the leguminosæ family.
The list[42] of plants in which saponin has been discovered is given in the note. All these plants are contained in the middle plane of Heckel's scheme. No plants containing saponin have been found among apetalous groups. No plants have been found containing saponin among the lower monocotyledons.
The plane of saponin passes from the liliaceæ and allied groups to the rosales and higher dicotyledons.
Saponin belongs to a class of substances called glucosides. Under the action of dilute acids, it is split up into two substances, glucose and sopogenin. The chemical nature of this substance is not thoroughly understood. The commercial[43] product is probably a mixture of several substances.
This complexity of chemical composition of saponin is admirably adapted for the nutrition of the plant, and it is associated with the corresponding complexity of the morphological elements of the plant's organs. According to M. Perrey,[44] it seems that the power of a plant to direct the distribution of its carbon, hydrogen, and oxygen to form complex glucosides is indicative of its higher functions and developments.
The solvent action of saponin on resins has been already discussed. Saponin likewise acts as a solvent upon barium[45] sulphate and calcium[46] oxalate, and as a solvent of insoluble or slightly soluble salts would assist the plant in obtaining food, otherwise difficult of access.