The alkaloid[35] furnishing families belong, with few exceptions, to the dicotyledons.  The colchiceae, from which is obtained veratrine, form an exception among the monocotyledons.  The alkaloids of the fungus have already been noted.

[36]Among the greater number of plant families, no alkaloids have been found.  In the labiatae none has been discovered, nor in the compositae among the highest plants.

One alkaloid is found in many genera of the loganiaceae; berberine in genera of the berberidaceae, ranunculaceae, menispermaceae, rutaceae, papaveraceae, anonaceae.

Waxes are widely distributed in plants.  They occur in quantities in some closely related families.

Ethereal oils occur in many families, in the bark, root, wood, leaf, flower, and fruit; particularly in myrtaceae, laurineae, cyperaceae, crucifereae, aurantiaceae, labiatae, and umbelliferae.

Resins are found in most of the higher plants.  Tropical plants are richer in resins than those of cold climates.

Chemical resemblance between groups, as indicating morphological relations, has been well shown.  For example:  the similarity[37] of the viscid juices, and a like taste and smell, among cactaceae and portulaceae, indicate a closer relationship between these two orders than botanical classification would perhaps allow.  This fact was corroborated by the discovery of irritable stamens in Portulaca and Opuntia, and other genera of cactaceae.

Darwin[38] states that in the compositae the ray florets are more poisonous than the disk florets, in the ratio of about 3 to 2.

Comparing the cycadeae and palmae, the former are differently placed by different botanists, but the general resemblance is remarkable, and they both yield sago.

Chemical constituents of plants are found in varying quantities during stated periods of the year.  Certain compounds present at one stage of growth are absent at another.  Many facts could be brought forward to show the different chemical composition of plants in different stages of growth.  The Thuja occidentalis[39] in the juvenescent and adult form, offers an example where morphological and chemical differences go hand in hand.  Analyses of this plant under both conditions show a striking difference.

Different parts of plants may contain distinct chemical compounds, and the comparative chemical study of plant orders comprises the analysis of all parts of plants of different species.

For example; four portions of the Yucca angustifolia[40] were examined chemically; the bark and wood of the root and the base and blades of the leaves.  Fixed oils were separated from each part.  These were not identical; two were fluid at ordinary temperature, and two were solid.  Their melting and solidifying points were not the same.

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.