'^^^^■'i CHEONOLOGICAL NOTES. 411 



all the trunks and stems in his collection, establishing new genera and 

 species based thereon, some of which are still accepted, as, e. g., Psar- 

 onius. He reduces the forms in which all vegetable remains occur to 

 three general classes, viz., (1) mere impressions without any remnant 

 of the original cause ; (2) petrifactions proper, in which the original 

 substance is replaced with precision by the particles which were in the 

 solution in which the plant was immersed ; and (3) true vegetable re- 

 mains whose substance is still present though somewhat metamor- 

 phosed, as, e. g., lignite. This classification may be profitably com- 

 pared with that of Schultze, in the work which has already been no- 

 ticed. "^ His BendroUthen embrace more than did Sprengel's Psaro- 

 lithi, and aimed to include all the objects of this general class with 

 which he was acquainted. 



Witham's "Internal Structure of Fossil Vegetables" (supra, p. 373), 

 appeared in 1833, and is the most exhaustive treatise thus far produced 

 ou the histology of paleobotany. He was evidently unacquainted with 

 Cotta's " Deudrolithen," and, so far as the work itself would indicate, with 

 Sprengel's " De Psarolithis." He confined his investigations entirely to 

 British fossils, to which he is able in most cases to apply the systematic 

 names given by Brongniart and Lindley and Hutton. The classifica- 

 tion adopted is that of Brongniart. He makes his study comparative, 

 aud devotes two plates to the illustration of the structure of various 

 kinds of wood of living trees. 



One other important work appeared in 1833, viz., Zenker's "Beitrage 

 zur Naturgeschichte der Urwelt," "" which, while describing animal re- 

 mains from several localities and horizons, devotes 23 of its 67 pages, 

 and three of the six plates to the description and illustration of the re- 

 markable Cretaceous plant beds of Blankenburg in the Harz district. 

 This memoir is remarkable for being the first attempt systematically to 

 treat dicotyledonous fossils, and notwithstanding the adverse fate which 

 has overtaken nearly all the names given at that and earlier periods to 

 plants of all kinds, Zenker's genus, Gredneria, still stands, and seems 

 likely to stand much longer, if not perpetually. Though less well 

 known than the CEningen leaf-prints, this locality was known to Scheuoh- 

 zer, Briickmann, and Walch, but its systematic study as well as the 

 initial step in the investigation of dicotyledonous fossil plants was re- 

 served for Zenker in the second quarter of the nineteenth century. 



The year 1834 would be sufficiently memorable in the annals of paleo- 

 botany if it had witnessed nothing more than the appearance of the 

 first memoir "^ relating to the subject, from the pen of Doctor Heinrich 



"9 Kurtze Betraohtung derer Krauterabdruoke im Steinreiche, pp. 7-9. 



180 Jonathan Carl Zenker. Beitrage zur Naturgeschichte der Urwelt, etc. Jena, 

 1833. 



-i"' Ueber die Bestrebungen der Schlesier die Flora der Vorwelt zu erlautern. Schle- 

 sisohe Provincialblatter, August und September, 1834. Also in Karsten undDechen's 

 Arohiv, Band VIII, 1835, pp. 232-249. 



