The wood was formed in closely packed radiating rows by a normal cambium (see [p. 66]), and the tracheæ so formed had characteristic rows of bordered pits (see [fig. 62B]). The wood comes nearer to that of the living Araucarias than any other, and indeed the numerous pieces of fossil wood of this type which are known from all the geological periods are called Araucarioxylon.[11] A double strand goes out from the main mass of wood, which afterwards divides and subdivides to provide the numerous bundles of the leaf.
Fig. 63.—Cast of Hollow Pith of Cordaites, the constrictions corresponding to discs of solid tissue across the cavity
In the case of these fossils we are fortunate enough to have the fructifications, both male and female, in a good state of preservation. As in other Gymnosperms, the male and female cones are separate, but they differed less from each other in their arrangement than do those of any of the living types hitherto mentioned. They can hardly be described as true cones, though they had something of that nature; the seeds seem to be borne on special short stems, round which are also sterile scales. In the seed and the way it is borne perhaps the Cordaiteæ may be compared more nearly with the Taxeæ than with the other groups. A seed, not yet ripe, is shown in slightly diagrammatic form in [fig. 64], where the essential details are illustrated. The seeds of this family sometimes reached a considerable size, and had a fleshy layer which was thick in comparison with the stone, and externally comparable with a cherry—though, of course, of very different nature in reality, for Cordaites, like Taxus, is a Gymnosperm, with simple naked seeds, while a cherry is the fruit of an Angiosperm.
In a few words, these are the main characters of the large group of Cordaites, which held the dominant position among Gymnosperms in the Palæozoic era. They have relationships, or perhaps one should say likenesses, to many groups. Their stem- and root-anatomy is similar to the Coniferæ of the present day, the position of the ovules is like that in the Taxaceæ, the male cones in some measure recall those of Ginkgo, the anatomy of their leaves has points which are comparable with those of the Cycads, to which group also the large pith in the stem and the structure of some details in the seeds unite them. Their own specially distinctive characters lie in their crown of huge leaves, and unbranched shaft of stem, the similarity of their male and female inflorescences, and some points in their pollen grains which have not been mentioned. The type is a very complex one, possibly coming near the stock which, having branched out in various directions, gave rise to several of the living families.
Fig. 64.—Representation of Cordaites Seed and its Axis with Scales, slightly diagrammatic, modified from Renault.
A, Axis with s, scales; c, coat of the seed, from which the inner parts have shrunk away; n, nucellus; p.c, pollen chamber containing pollen grains which enter through m.
Plants which come very near to the Cordaiteæ are the Poroxyleæ. Of this group we have unfortunately no remains of fructifications in organic connection, so that its actual position must remain a little doubtful till they are discovered. There seems no doubt that they must have borne seeds.
Still, it has been abundantly demonstrated in recent years that the anatomy of the root, stem, and leaves indicates with considerable exactness the position of any plant, so that, as these are known, we can deduce from them, with a feeling of safety, the position that Poroxylon takes in the natural system. In its anatomy the characters are those of the Cordaiteæ, with certain details which show a more primitive nature and seem to be characteristic of the groups below it in organization.