PSARONIUS 297 



highly complex polystelic organisation, comparable to 

 that of the most highly differentiated Fern- stems of 

 our own day. The structure of the Psaronii has been 

 worked out in a most elaborate manner by Corda, 

 Goppert, and Stenzel in Germany, and by Zeiller and 

 Renault in France. A very full description, covering 

 many species and forming a model of fossil anatomical 

 investigation, is that given by M. Zeiller in the first 

 volume of the magnificent work, so often referred to, 

 on the fossil flora of Autun and Epinac. 1 M. Zeiller, 

 discarding the somewhat complex methods of arrange- 

 ment of earlier authors, classifies the members of the 

 genus according to their phyllotaxis, ranging them in 

 three groups — the Polystichi, with numerous vertical 

 series of leaves ; the Tetrastichi, with four such series ; 

 and the Distichi, with only two. The illustration in 

 Fig. 1 1 3 is taken from one of the Tetrastichous division ; 

 this group is the least important of the three in number 

 of species, but the form selected, Psaronius brasiliensis , 

 Brongn., shows the anatomical structure with remarkable 

 clearness. This fossil, as its name shows, came from 

 Brazil, and, though its source is still uncertain, is 

 probably of Permian age, like the majority of the 

 European species. 



The stem, as in all the Psaronii, is made up of 

 two well-defined regions — a central portion, including 

 the whole of the vascular system proper to the stem, 



1 Corda, Beitrdge zur Flora der Vorwelt, Prague, 1845 > Goppert, 

 " Die fossile Flora der Permischen Formation," Palaeontographica, vol. 

 xii. 1864; Stenzel, " Ueber die Staarsteine," Nova Acta, vol. xxiv. 1854; 

 Zeiller, Bassin houiller et permien oVAutun et d Epinac, vol. i. 1890 ; 

 Rudolf, "Psaronien und Marattiaceen," K. K. Akad. d. Wiss. Vienna, 

 .1905; Stenzel, "Die Psaronien," Beitr. z. Palaont. u. Geol. Oesterreich- 

 Ungarns, 1906. 



