The unsatisfactory condition of palæontological botany arises from the imperfect materials which are obtained from the earth's strata. With the exception of two or three remarkable structures, no histological characters have been found whereby the position of a plant can be determined from an examination of its woody structure; so that silicified or calcified woods, which are far from rare, supply little more information than that they are portions of a vascular cryptogam, a palm, a conifer, or other exogen. Of leaves also it may be said that, while a very few natural families have characteristic forms, yet leaves which are undistinguishable are found belonging to plants widely separated in the vegetable kingdom, so that we have little confidence in determinations made from them; indeed, such determinations must be consideredat the best but as guesses at the truth, and these can seldom go further than the natural order, or, perhaps, the genus towhich the fossil belongs. To manufacture species on no other characters than those obtained from slight variations in the form of the leaf, is a reckless multiplication of names, condemned not only by the botanist, but by every one who has carefully examined the variety in form and venation that exist among the leaves of a single shrub or tree. The organs employedby systematists in the classification of plants are so delicate, and so easily perish, that they are very rare as fossils.Fruits, however, are more abundant, and after the flower they may be held of next value in determining the affinities of aplant. Even the separated seeds of living species, or members of living genera, can be positively determined; but when the affinities are obscure, the more or less imperfect specimens of fossil seeds detached from their fruits are very unsatisfactory materials.