CONTRIBUTIONS FROM THE PHANEROGAMIC LABORATORIES

OF HARVARD UNIVERSITY. NO. 55.

THE HISTORY, COMPARATIVE ANATOMY AND EVOLUTION OF THE ARAUCARIOXYLON TYPE.

BY EDWARD C. JEFFREY.

Received, September 28, 1912.

PART I.

FOSSIL woods of the Araucarioxylon type are extremely abundant in the Mesozoic deposits. The only living conifers with wood of this type are confined to the Eastern tropical region, to Australasia and to South America and are all included under the two genera Agathis and Araucaria. As a consequence of their habit, which differs from that of all living Conifers, except certain of the Podocarpineae, and of the organization of their woody tissues, the Araucarian Conifers have been most commonly referred to affinities with the Cordaitales, an important gymnospermous group of the Paleozoic. As will be shown in connection with the present investigations, the importance of these features of resemblance has apparently been much exaggerated. The association with the Cordaitales carries with it the implication, that the Araucariineae are either the ancestors of the other existing coniferous tribes, as is quite commonly held, or else that they constitute a separate line of descent, distinct from the ancestral stock of the remaining Conifers, as has been maintained in recent years by Seward and Penhallow. It is obviously a matter of considerable importance to clear up the affinities of the Araucarian stock, not only from the standpoint of its particular origin; but on account of the light thus to be thrown on the vexed subject of evolutionary processes as a whole by reason of the abundant display of the group during so long a period of geological time. The present writer has devoted nearly ten years to the procuring of material of Araucarian Conifers living and extinct and to the developmental, experimental and comparative anatomical investigation of their various organs and tissues.

It cannot be too strongly emphasized in connection with the present work, that general principles in biology are either of universal validity or of little scientific value, and that they cannot in certain cases be admitted and in others denied. There can be little doubt moreover that not attle of the existing reaction against the hypothesis of evolution, is the result of a failure on the part of biologists to apply evolutionary principles clearly, consistently and logically to the elucidation of their investigations, even if only from the standpoint of a working hypothesis. It seems clear that either there are generally valid biological principles, as there are commonly accepted principles in chemistry, physics and the other cognate sciences, or that biology has either not yet reached the scientific stage of development or has ceased to exist on the scientific footing. There appears to be no reason to adopt either of the latter alternatives. Darwin in the prolegomena to his Origin of Species, emphasized the importance of the data supplied by development, history, comparative anatomy and geographical distribution in connection with the study of evolutionary processes in living beings. Since Darwin's time experimental methods have come largely into the foreground and there can be little doubt that evidence derived from this source, especially when controlled by an adequate knowledge of the geological history of beings now living, is of paramount importance. It is proposed in the series of articles of which this is the first, to discuss the origin, affinities and evolution of the Araucarian Conifers, so far as appears profitable, along all the important lines of investigation, indicated above.

It will be convenient here to define the Araucarioxylon type of wood. In the mature secondary wood of the trunk in the living Araucaria and Agathis, we find certain peculiarities, which are taken together unique among living conifers. The tracheids in these two genera are characterized by the presence of pits, which are closely approximated and flattened, or where they occur in two or more rows, alternating in their arrangement and polygonal in their form. The wood of the Araucarian type in respect to its pitting resembles in a marked degree that of the Cordaitales. The remaining tribes of existing Conifers possess a type of tracheary pitting in which the pores are rarely or never closely contiguous and when in several rows are opposite and not alternating. The pits in this type too are often separated by cellulose bars running transversely across the lignified walls of the tracheids and imbedded in their substance. These bars of Sanio are absent in the Araucarian conifers. They should not be confused 1 Gerry, Eloise, The Distribution of the Bars of Sanio in the Coniferales. Ann. Botany, 24, p. 231.

with the trabeculae of Sanio, lignified processes, crossing the lumen of the tracheids, common to the Gnetales, Coniferales and a few Angiosperms. Another feature of the Araucarioxylon type is the usual absence of wood parenchyma and the smooth walled character of the ray cells. The last two features are less typical than the ones mentioned above since they are shared to a considerable extent by the woods of the remaining tribes of Coniferales. The last character has had recently assigned to it an apparently exaggerated importance.2 Gothan has recently referred woods, which are strikingly Araucarian in the aggregate of their characteristics, to abietineous affinities on account of their strongly pitted rays, apparently losing sight of the fact that pitted rays occur commonly or sporadically in all the tribes of Conifers. The present article is to be devoted to the historical, comparative anatomical and experimental study of the rays and wood parenchyma in the Araucarian Conifers.

Beginning with the historical aspect, Figure a, Plate 1, shows the character of the pitting in the tracheids in an Araucarian wood of the Upper Jurassic, to be described in detail on another occasion. The pits are numerous and in several rows, with the marked alterna tion, characteristic of the Araucarioxylon type. They are not however as closely approximated as is the case with the pits in the tracheids of the adult wood of the living genera Araucaria and Agathis. Figure b, Plate 1, illustrates the ray structure in the same wood. It is clear that the cells of the ray, in contact with one another are very strongly pitted, exactly for example as is commonly the case in the rays of the Abietineae. On account of the pitting of the rays in woods of this type from the Upper Jurassic of King Carl's Land 3 and of the island of Spitzbergen Gothan has recently referred them to abietineous affinities. It is to be pointed out in this connection that Seward has considered woods of a similar type from the Upper Lias of Yorkshire in England to belong to the Araucarian conifers. Moreover Lignier more recently has described woods of a similar or nearly similar horizon, as likewise of Araucarian affinities. About the same time

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2 Gothan, Zur Anatomie lebender u. fossiler Gymnospermen-Hoelzer; Abh. d. Koenig. Preuss. geolog. Landesanstalt; Neue Folge, Heft 44, Berlin (1903).

3 Gothan, Fossilen Hoelzer von Koenig Karl's Land, Kung Svensk. Vetenskap. Handlingar, Bd. 42, No. 10.

4 Gothan, Fossilen Holzreste von Spitzbergen, Kung. Svensk. Handlingar, Bd. 45, No. 8.

5 Cat. of Mesozoic Plant, Brit. Museum, Jurassic Flora, Pt. 2, pp. 56, 57, pls. 6, 7, London (1904).

60. Lignier, Végétaux Fossiles de Normandie, IV. Bois Divers (Ire. Série), Caen (1907).

the present writer described woods of a similar type with a similar expression of affinities from a horizon, variously estimated from Middle to Lower Cretaceous, displayed at Kreischerville, Staten Island, N. Y.7 It will be noted that the weight of opinion is against Gothan, in the matter of the reference of woods Araucarian in other respects, which have the strongly pitted rays of the Abietineae, to affinities with that tribe of Conifers, since Professor Seward, Professor Lignier and the writer agree in retaining them with the Araucariineae. Since a correct scientific verdict, however, does not depend on majorities, it will be well to investigate the matter from other standpoints.

A fundamental doctrine of Biology, owing its origin primarily to the deductive methods of the philosopher rather than to the more severe inductive procedure of the sciences, but since strongly confirmed by purely inductive data, is the doctrine of recapitulation. While it is undoubtedly the case that the seedlings and sporelings of the higher plants vouch in the strongest way for the validity of the recapitulation hypothesis, we have on the vegetable side corollaries to that doctrine, not illustrated as a rule by animals. There are organs of the plant for example, even more strongly retentive of ancestral characters than the seedling stem. Perhaps the most conservative organ is the root, which varies so little in its fundamental organization throughout the vascular plants, that one formula will represent the organization of all roots. In the case of the Gymnosperms and other typically coniferous groups, the axis of the cone has likewise been found to be strongly retentive of features which have disappeared entirely in the vegetative stem. Figure c, Plate 1, shows the inner region of the woody cylinder of the cone of Agathis australis, in transverse section. It is clear that the cells of the wood rays are in contrast to the typical condition for living Araucarian Conifers, very strongly thickened and even in this unfavorable plane of section, obviously pitted. We have in other words a condition present like that found in certain Jurassic and Lower Cretaceous woods which have been referred by the majority of paleobotamists, who have specially investigated them, to Araucarian affinities. Gothan however as pointed out above, places them on account of their thickened and strongly pitted ray-cells among the Abietineae. Figure d, Plate 1, shows a vertical section of one of the rays of the cone of Agathis australis, from which the contents have been removed in order that the sculpture

7 Araucariopitys, a new genus of Araucarians, Bot. Gaz., 44, 1-15, pls. 27-30, (1907).