I. On the comparative anatomy and affinities of the araucarineœ

Abstract
The simple anatomical structure of the Araucarineae is variously interpreted by botanists. The group was regarded until recently as the one family of Conifers whose connection with the Cordaiteae of the Palaeozoic was at all intimate. This view of their relationship, which is by no means at present abandoned, was based chiefly on a resemblance in gross morphology of leaf and stem and on two anatomical features— the absence from both groups of any specialised resiniferous tissue in their secondary wood and the presence in both of alternate rows of hexagonal pits on the tracheids of this wood. Dr. Scott stands as perhaps the most convinced adherent of the Cordaitean ancestry of the Araucarineae, in spite of the recent works of Jeffrey and Seward, which tend, from different standpoints, to annul the validity of the relationship between them. These investigators both recognise that the structure. of the Araucarinese is of a very simple type, though each interprets the simplicity in a very different way. Prof. Jeffrey considers the Abietinese the most ancient of the living Conifers and the most closely associated with the Cordaitean forms, and regards the Araucarinese as having been derived from them in comparatively early geological times. According to his view the ancestral Araucarians had leaves borne on spur shoots like the pines of to-day. The simplicity of the wood structure of the Araucarinese, too (multiseriate pitting and absence of specialised secretory tissue), is not indicative of Cordaitean affinity but has been acquired a second time from the pine alliance with opposite pitting and complex horizontal and vertical systems of resin canals. Prof. Seward, on the other hand, regards the Araucarinese as derived from Lycopod stock, and in his and Miss F ord’s (1906) account of the group states the evidence in favour of interpreting the simple structure of the Araucarinese in terms of this connection. According to Seward’s view, the simplicity of structure is an indication of primitive organisation, while according to Jeffrey’s it is in the nature of a specialisation. Moreover, Jeffrey, in reading specialisation into the structure of the Araucarinese, and in calling in question their connection with the Cordaitese, has done much to permit the Lycopod theory of the ancestry of the Conifers to become the rival of the Cordaitean. This is the more evident when it is realised how imperfectly his Abietinean substitute bridges the anatomical gap between the Conifers and the Cordaitean forms—with practically no crucially important structural feature in common between them. One need only recall in this connection the contrast between the secondary wood of the two groups in such fundamentals as pitting, ray structure, and resin tissue. Indeed, the resin tissue in itself would seem to present an impassable gulf. Over this, too, Jeffrey has not attempted to construct a bridge; his theory postulates the presence of horizontal and vertical resin canals in the secondary wood of the ancestral Abietinese, without even a suggestion as to the origin of these canals, and yet the Cordaitean forms, which he regards as the ancestors of the Abietinese, and with which the latter are supposedly the most closely connected of the Conifers, are devoid of such structures. Scott (1909, pp. 653-657), in presenting the evidence in favour of the Cordaitean versus the Lycopod ancestry of the Araucarinese, does not refer to J effrey’s theory, which, if correct, renders the one—and possibly the greater, the constructive—part of his argument groundless. Thus, as the problem stands at present, the writer considers that any evidence that tends to overthrow the Abietinean theory of the ancestry of the Araucarineae and to strengthen the connection of this family with the Cordaitean alliance, makes the case doubly strong against the Lycopod theory.

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