Physiologie. — Palaeontologie. 187 



tisinsäure nicht zurückzuführen war. Denn es fand sich Tyrosin im 

 Saft nur in so geringer Menge vor, dass diese Aminosäure einen 

 wesentlichen Anteil an der Dunkelfärbung nicht haben konnte. 

 Homogentisinsäure vermochte V^erf. überhaupt nicht nachzuweisen. 



O. Damm. 



Wieland, G. R., American Fossil Cycads. (The Carnegie Insti- 

 tution of Washington. XVIII. 296 pp. pl. I-L. 1906.) 



This large and finely illustrated volume is the resuit of work 

 which has been in progress since 1898, when the initial field work 

 was undertaken; but the author directs attention to the fact that 

 the results so far reached relate wholly to the more obvious boun- 

 daries and botanical aspects of the Cycads, rather than to their 

 Classification and nomenclature, which must be reserved for future 

 consideration ; while a yet further question of great biological 

 interest is to be found in the detailed structure of the seed. 



The first cycadean trunks from America to receive scientific 

 mention, were obtained from the Potomac formation of Maryland 

 and were noticed bj^ Philip Tyson in 1860, but for twenty-five years 

 no further notice was taken of them. In 1889, however, several of 

 these specimens were described in accordance with their macro- 

 scopic characters, and since that time there has been a constantly 

 increasing interest in this group of fossils which has reached its 

 culmination in the work on the large collections to be found chiefly 

 in the Yale Museum. A special impetus w^as given to this work 

 when, in 1893, the first Cycads from the Black Hills were descri- 

 bed, an through the later work of T. H. Mac Bride, Prof. Lester 

 F. Ward and Prof. O. C. Marsh there was brought together a 

 very remarkable series of specimens embracing twenty-nine species 

 as defined by Ward on the basis of their external characters, and 

 b}' him assigned to the genus Cycadeoidea of Buckland. All of 

 these specimens were obtained from seven localities in Wyoming 

 and South Dakota. 



Another locality for Cycads, is found in the Freezeout Hills 

 of Carbon County, Wyoming. The age of these deposits is 

 regarded as Upper Jurassic, and therefore the same as for 

 the specimens previously noted; but instead of yielding Cycadeoidea, 

 the beds contain only Cycadella of which 29 species have been 

 recognized. 



Within the boundaries north of Mexico, there are ten recogni- 

 zed localities yielding the remains of Cycads, and these represent 

 horizons ranging from the Trias of Prince Edward Island and 

 Pennsylvania, to the Upper Cretaceous of Colorado; but 

 the greatest development of these plants appears to have been 

 attained in the Jurrassic where we meet with the greatest numerical 

 representation as well as the greatest specific diversification. 



The author makes comparison with European localities of which 

 he enumerates eight, and introduces a useful summary of the Old 

 World types showing their source, geological horizon and other 

 useful details. It is shown that the geological ränge is the same, in 

 general terms, as for the American species. 



The author treats his material in an exhaustive manner within 

 the limits assigned, and it will suffice to indicate the ground covered 

 by citing the general subjects discussed: 



I. Discoveries and Collections. II. Preservation and external cha- 



