The student of palaeobotany has perhaps to face more than his due share of difficulties and fruitful sources of error; but on the other hand there is the compensating advantage that trustworthy conclusions arrived at possess a special value. While always on the alert for rational explanations of obscure phenomena by means of the analogy supplied by existing causes, and ready to draw from a wide knowledge of recent botany, in the interpretation of problems furnished by fossil plants, the palaeobotanist must be constantly alive to the necessity for cautious statement. That there is the greatest need of moderation and safe reasoning in dealing with the botanical problems of past ages, will be apparent to anyone possessing but a superficial acquaintance with fossil plant literature. The necessity for a botanical and geological training has already been referred to in a previous chapter. It would serve no useful purpose, and would occupy no inconsiderable space, to refer at length to the numerous mistakes which have been committed by experienced writers on the subject of fossil plants. Laymen might find in such a list of blunders a mere comedy of errors, but the palaeobotanist must see in them serious warnings against dogmatic conclusions or expressions of opinion on imperfect data and insufficient evidence. The description of a fragment of a handle of a Wedgwood teapot as a curious form of Calamite[137] and similar instances of unusual determinations need not detain us as examples of instructive errors. The late Prof. Williamson has on more than one occasion expressed himself in no undecided manner as to the futility of attempting to determine specific forms among fossil plants, without the aid of internal structure[138]; and even in the case of well-preserved petrifactions he always refused to commit himself to definite specific diagnoses. In his remarks in this connection, Williamson no doubt allowed himself to express a much needed warning in too sweeping language. It is one of the most serious drawbacks in palaeobotanical researches that in the majority of cases the specimens of plants are both fragmentary and without any trace of internal structure. Specimens in which the anatomical characters have been preserved necessarily possess far greater value from the botanist’s point of view than those in which no such petrifaction has occurred. On the other hand, however, it is perfectly possible with due care to obtain trustworthy and valuable results from the examination of structureless casts and impressions. In dealing with the less promising forms of plant fossils, there is in the first place the danger of trusting to superficial resemblance. Hundreds of fossil plants have been described under the names of existing genera on the strength of a supposed agreement in external form; but such determinations are very frequently not only valueless but dangerously misleading. Unless the evidence is