An account of phytochemical substance has been provided by Wiesner’s Rohstoffe des Pflanzenreichs, arranged by products, another account has been given by Karrer, compounds of established constitution arranged according to a chemical system. Though useful, none of these works, including also those of Czapek and Wehmer, aims, however, to use phytochemistry as an auxiliary branch of plant taxonomy. It does seem necessary here to stress in a concise way the importance of the subject for taxonomy. All of us have used some coarse phytochemical characters, looked at characteristic glands and crystals, observed and used colours of dried leaves, tasted plants for bitter substances, sniffed at aromatic oils, and other secondary compounds. The use of these characters as arguments for taxonomic purpose has, however, been erratic and only been employed if very obvious and/or abundant. Everyone of us looked for refinement of the aspect. This is the principal aim of the present endeavour.