In recent years it has been customary to assign Palaeozoic wood with Araucarian pitting to the genus _Dadoxylon_, while wood of the same general type from more recent strata is by many authors referred to _Araucarioxylon_[650]. This arbitrary distinction based on a difference in age is open to serious objection. Fossil wood of the Araucarian type is widely scattered in strata ranging from Carboniferous to Jurassic periods; it also occurs in later formations. The fact that on the one hand Araucarian plants, as recognised by cones and foliage-shoots, are especially characteristic of Jurassic floras and occur more rarely in Rhaetic and Triassic floras, and on the other hand that _Cordaites_ and its allies reached their greatest development in Permo-Carboniferous times, renders it probable that in the majority of cases a distinctive name based on geological age would be in accordance with botanical differences. But we have no satisfactory data as to the upper limits of the Cordaiteae or the lower limits of the Araucarineae: in all probability the two families overlapped and co-existed for more than one geological period. It is, moreover, the plants from formations where overlapping occurred that are the most critical from a botanical standpoint. The age-distinction is therefore at best an artificial one and may be seriously misleading. Potonié[651] and Gothan[652] have emphasised the desirability of adopting the name _Dadoxylon_ for all wood of the Araucarian type irrespective of age. If a particular specimen can be correlated definitely with _Cordaites_ or some other genus it should be so designated, but the fragmentary nature of the records usually precludes this simple course. The most logical plan is to use the name _Dadoxylon_ for all woods with Araucarian characters if there is no sufficient reason for employing a less provisional term. If the evidence clearly points to the Araucarineae the generic name _Araucarioxylon_ should be added in parentheses after _Dadoxylon_, but whether or not this is done, a statement as to the geological age of the fossil will in itself be some assistance in enabling the student to form an opinion on the balance of probability in favour of a Cordaitean or an Araucarian affinity. The course suggested by Gothan[653], namely to add _Cordaites_ after _Dadoxylon_ if an _Artisia_ pith is present, is rendered inoperative now that we know that a discoid pith occurs in more than one genus. In this chapter we are concerned primarily with _Cordaites_ and with such stems as may fairly be regarded as Cordaitean: examples of fossil wood from later formations are dealt with in another place. A distinction between _Araucarioxylon_ and _Cordaioxylon_ stems has been based by Felix on the nature of the pith-casts; those of the _Artisia_ type he refers to _Cordaioxylon_, while Palaeozoic stems with _Tylodendron_ pith-casts are assigned to _Araucarioxylon_[654]. This distinction can, however,