ABSTRACT
The systematist dealing with Bacteria is obliged, from the extreme simplicity of their observable structure, to make extensive use of physiological and biochemical characters; such characters undoubtedly have classificatory value in higher animals and plants also. This chapter considers briefly the present and the potential classificatory value of biochemical, physiological, and behavioural characters. The dividing lines between the different types of non-structural information which may have classificatory value are, of course, arbitrary, cutting through the unity of the organism. Chemical evidence may also be used to clarify relationships within particular families of Angiospermae. Relationships within and between genera have also been investigated on a basis of chemical evidence. Comparative physiology has been a fairly popular denomination among zoologists and botanists for a long time, but very few of those who called themselves comparative physiologists have made any significant contribution to the systematic ordering of the sort of information in which they deal.
