Contributions to the Anatomy of Mesozoic Conifers No. 2. Cretaceous Lignites from Cliffwood
One of the most interesting and, at the same time, most disputed questions in the phylogeny of the Coniferales deals with the relative antiquity of the abietineous and araucarian lines. The general ligneous structure of the latter has led the majority of botanists to its direct affiliation with the Cordaitales. In a recent paper, Professor JEFFREY2 has shown that this resemblance exists only in the normal mature wood, and that in the seedling stem, root, cone axis, and traumatic tissue, there
... tic tissue, there are present altogether different conditions. In these regions the rays often become thickwalled and heavily pitted, there are wood parenchyma cells, and the tracheary pits, instead of being closely approximated, are scattered and opposite. Moreover, in the cone axis the pits are separated by well marked cellulose bars of Sanio. All these features are characteristic of the Abietineae, and diametrically opposed to anything found in the Cordaitales. The locality of these digressions from the Araucarioxylon type is of especial significance. On both the zoological and botanical sides, the law of recapitulation is regarded as one of the fundamental conceptions of evolution, and according to this law it is in the plant seedling that ancestral features should be found. Further, case after case has been recorded where these primitive conditions are retained in the root and reproductive axis, and recalled in traumatic tissue. As I Contributions from the Phanerogamic Laboratories of Harvard University, no. 63. 2 JEFFREY, E. C., The history, comparative anatomy, and evolution of the Araucarioxylon type. Proc. Amer. Acad. 48:53I-57I. pis. 7. I9I2. Botanical Gazette, vol. 58] [I68 This content downloaded from 129.100.058.076 on October 12, 2016 09:01:08 AM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-I9I4] HOLDEN-CRETACEOUS LIGNITES 169 instances of the first may be mentioned the occurrence of resin canals in the center of the root of such conifers as A bies and Tsuga, a harking back to the time when they were scattered throughout the wood, as in Pinus; as instances of the second, the presence of centripetal wood in the cone axis of Equisetum; and of the last, the ray tracheids in wounded specimens of Abies. It seems clear, therefore, from comparative anatomical and developmental evidence, that the Araucarineae are descended from ancestors which had thick-walled pitted rays, wood parenchyma, and scattered tracheary pits separated by bars of Sanio. These hypothetical ancestors are probably the Abietineae. If such a conclusion is correct, we should expect to find fossil record of woods which possessed these modified araucarian structures, not only in primitive places, but also in their normal, mature growth. Recent investigation has shown such to be the case. For example, Araucarioxylon Lindleyi Seward, Cormaraucarioxylon crasseradiatum Lignier, and Araucarioxylon noveboracense Jeffrey have wood parenchyma; Cormaraucarioxylon crasseradiatum Lignier, Protocedroxylon araucarioides Gothan, and Araucariopitys americana Jeffrey have thick-walled pitted rays. Further, many of these Mesozoic araucarians have traumatic resin canals, as do A bies, Cedrus, etc. Up to the present, however, no fossil araucarian has been described with opposite pits or bars of Sanio. In an earlier paper3 the writer has described several species of Pityoxylon from the Raritan Cretaceous of Cliffwood, New Jersey. These were included in a considerable amount of lignite collected by Professor JEFFREY, and turned over to the writer for investigation. In addition to the Pityoxyla, there were a number of Cupressinoxyla, and one Araucarioxylon. This last specimen was of especial interest in this connection, and will accordingly be described first. The material consisted of a flattened stem about two inches in length and one in diameter. The preservation of the outer layer was but indifferent; near the center, however, it was excellent. The pith contains large masses of stone cells, similar to those of the living Agathis. Fig. i represents a radial section of the wood at 3 HOLDEN, RUTH, Cretaceous Pityoxyla from Cliffwood, New Jersey. Proc. Amer. Acad. 48:609-623. pIs. 4. I913. This content downloaded from 129.100.058. Summary i. An Araucarioxylon from the Raritan Cretaceous of Cliffwood, New Jersey, shows bars of Sanio near the pith of the stem, similar to those on the cone axis of the living Araucarineae. 2. Brachyoxyla from the same locality are as a rule very similar to those from Kreischerville, Staten Island, differing only in such details as arrangement of medullary sclerites and structure of the bast. 3. The Cupressinoxyla of Cliffwood all lack cellulose bars of Sanio in the mature wood, and should on that account be placed in the new genus Paracupressinoxylon. 4. The occurrence of three absolutely typical Pityoxyla, and not a single typical Araucarioxylon, among these lignites seems to indicate that in tracing back the families of living conifers it is the Abietineae which remain unchanged, and the Araucarineae which become less and less like living representatives of that family. The same conclusion may be drawn from a consideration of the lignites of Staten Island. a. The variety of structure of these Mesozoic araucarians has its bearing on the question of the monophyletic or diphyletic origin of the Coniferales. There are certain features which have been supposed to sharply differentiate the araucarians from the other families. Both fossil and comparative anatomical evidence demonstrate the fallacy of this view. As regards wood structure, every feature of the Abietineae-resin canals, bars of Sanio, thick-walled pitted rays, wood parenchyma (terminal and diffuse), even to as small and unimportant details as fusion pits in the rays and regularlv-alternating bands of hard and soft bast-has been found in the Araucarineae, living or extinct. As regards strobilar anatomy, EAMES7 has shown that the stages in the reduction of the female cone are closely paralleled in various cupressineous and taxodineous genera, and the writer' has shown that in one Mesozoic araucarian (Voltsia) there was a double cone scale, like that of the living genus EAMES, ARTHUR J., The morphology of Agathis astralis. Ann. Botany 27:i-38. pIs. I-4. I913. HOLDEN, RUTH.