96 



THE GEOLOGICAL HISTORY OF PLANTS. 



to the genus Zygopteris of Schimper. The central axis alone has a 

 curious resemblance to the peculiar stem described by Unger (" De- 

 vonian Flora of Thuringia ") under the name of Cladoxylon mira- 

 bile ; and it is just possible that this latter stem may be the axis 

 of some allied plant. The large aerial roots of some modern tree- 

 ferns of the genus Angiopteris have, however, an analogous radiating 

 structure. 



The specimen is from the collection of Berlin H. Wright, Esq., 

 of Penn Yan, New York, and was found in the Portage group (Upper 

 Erian) of Milo, New York, where it was associated with large petioles 

 of ferns and trunks of Lepidodendra, probably L. Chemungense and 

 L. primcevum. 



The occurrence of this and other stems of tree-ferns in marine 

 beds has recently been illustrated by the observation of Prof. A. 

 Agassiz that considerable quantities of vegetable matter can be 

 dredged from great depths in the sea on the leeward side of the 

 Caribbean Islands. The occurrence of these trunks further connects 

 itself with the great abundance of large petioles (Rhachiopteris) in 

 the same beds, while the rarity of well-preserved fronds is explained 

 by the coarseness of the beds, and also by the probably long macera- 

 tion of the plant-remains in the sea-water. 



In connection with this I may refer to the remarkable facts re- 

 cently stated by Williamson* respecting the stems known as Hete- 

 rangium and Lyginodendron. It would seem that these, while having 

 strong exogenous peculiarities, are really stems of tree-ferns, thus 

 placing this family in the same position of advancement with the 

 Lycopods and Equisetacem of the Coal period. 



IV. — On Erian Trees of the Genus Dadoxylon, Unger. 

 (Araucarites of Goeppert, Araucarioxylon of Kraus.) 



Large woody trunks, carbonised or silicified, and showing wood- 

 cells with hexagonal areoles having oval pores inscribed in them, 

 occur abundantly in some beds of the Middle Erian of America, and 

 constitute the most common kind of fossil wood all the way to the 

 Trias. They have in the older formations, generally, several rows 

 of pores on each fibre, and medullary rays composed of two or more 

 series of cells, but become more simple in these respects in the Per- 

 mian and Triassic series. The names Araucarites and Araucarioxy- 

 lon are perhaps objectionable, inasmuch as they suppose affinities to 

 Araucaria which may not exist. Unger's name, which is non- 



* "Proceedings of the Koyal Society," January 6, 1887. 



