Biochemical Systematics by Ralph E. Alston; B. L. Turner

The more we learn about biology the more we find out that all creatures contain the same basic components. This is bad for biochemical systematics. However, we have also learned that there are special compounds, deluxe equipment, nonessential to the welfare of the plant, which are peculiar and unique to an individual species, a group, a genus, or a family. It is these nonubiquitous materials, these compounds produced at the plant's whim rather than for its essential well-being, that constitute the subject matter of plant biochemical systematics.