G. Ii. Wieland — Williamsonian Tribe. 433 



Art. XLVII. — On the Williamsonian Tribe • by G. R. 



Wieland. 



(A preparatory study published by permission of the Carnegie Institution 

 of Washington.) 



To show bow the investigation of tbe Cycadophyta in both 

 field and laboratory, following the elaboration of the flowers of 

 Cycadeoidea a dozen years ago, has established the long prob- 

 lematic genus Williarnsonia as tbe type of a great and dom- 

 inant Mesozoic group, to further bring together, perhaps for 

 the first time, the data indicating the general alignment of this 

 group, and to give in plain form the story of its discovery, with 

 its principal structural features and something of their bearing 

 on plant evolution, is the object of the present preparatory 

 study. Obviously in so dealing with an alliance in the initial 

 stages of discovery, it is convenient to speak of it as a tribe for 

 the very reason that as used in science this term is an elastic 

 one ; though as here employed the larger sense as an aggregate 

 of diverse families, rather than of genera or subfamilies, is the 

 one inferred. Also the silicified cycads as named the Cycade- 

 noideae by Robert Brown in 1828 are arbitrarily separated from 

 the family Williamsonise, Carruthers 1870(5),* although no very 

 distinct line of demarcation appears. And, too, in singling out 

 the genus Williarnsonia as the group type, regard is had only 

 for the order of discovery ; it being important to point out 

 that this genus is by no means the most interesting form, — that 

 distinction unquestionably belonging to Wielandiella of the 

 Rhat of Shone, as so ably and skilfully studied by Professor 

 JSTathorst (21, 25), by means of the collodion film method 

 brought into practice by him and destined to play an impor- 

 tant role in all future study of fossil plants. 



It is but a few years since it was accepted with little thought 

 of question that tbe common types of Mesozoic cycadophytean 

 leaves must all pertain to plants belonging to true cone and 

 carpellary-leaf bearing Cycads near to existing types, or at least 

 to ancestral forms of strictly Cycadalean aspect. True enough, 

 Williamson (4), from long study of the specimens collected by 

 himself and his father along the Hawsker and Runswick cliffs 

 of the Yorkshire coast early in the last century, had reached, 

 about 1870, an excellent restoration of his "riddle" Zamia 

 gigas, — renamed Williarnsonia gigas by Carruthers (5). But, 

 as Carruthers had meanwhile found, the Isle of Wight silici- 

 fied trunk Bennettites Gibsonianus had an ovulate fructification 

 so different from other gymnosperms that its characters sug- 

 *See list of authors cited given at the end of this article. 



