The nature of lignin.

A review of the work done in the investigation of lignin as recorded in the voluminous literature on the subject, must certainly convince one of the difficulties involved in this great problem, and also show most plainly that, although a vast amount of careful research has been done, the question of the constitution of lignin, and its relation to the other constituents of the plant, is still unsettled. The study of the physiology of plants tells us that, in the course of growth, certain tissues are deposited in regular order, beginning with the primary body; the process is one of gradual evolution, and we do not meet with abrupt changes at any stage of the development. [...