﻿28 INTRODUCTORY. 



Transversely elliptical trunks. — It has at various times been suggested or 

 believed that some of the Cycadeoidete were characterized in life by a more or less 

 uniform transverse elliptieity. This idea seems to have originated with Robert 

 Brown, who stated in 1851 (15) that his specimens of Cycadites "all agreed in hav- 

 ing an elliptical outline unaccompanied by any inequality in the wood}' ellipsis." 

 Later, Carruthers (24), in founding for these and several other specimens his 

 genus Benncttites, distinctly assigns transverse elliptieity as one of the generic char- 

 acters. Since the work of Carruthers this character has been either cited (157), 

 doubted (144), or left in abeyance as requiring further examination (113). But it 

 is again recalled by Lignier's recent description of Cycadeoidea micromyela (84), the 

 tvpe of which, although flattened by pressure, shows distinct transverse elliptieity 

 of its medulla and xylem in a direction oblique to the only pressure plane noted. 

 It only needs to be pointed out that, as Lignier suggests, this specimen may be a 

 branch of a larger trunk. As such it may have been slightly flattened in life. But 

 when a large number of both branching and non-branching trunks fairly represent- 

 ing the Cycadeoidean series is examined, it at once becomes obvious that none of 

 the Cycadeoidese ever developed a normally compressed habit of trunk growth. 



In the first place, the trunks of the genus Cycadella, histologically speaking, 

 afford an example of one of the most beautifully preserved series known; yet they 

 have suffered more vertical, lateral, or other distortion than any other American 

 specimens, these trunks, with but a few exceptions, being compressed to from two- 

 thirds to one-half of their original thickness. Nevertheless, in any but the largest 

 thin sections the results of compression are but little noticeable. 



Again, in Cycadeoidea Jenney ana and C. iugens, as so well represented in the Yale 

 collection by fully 250 Black Hawk specimens, fragmentary and complete, we have 

 an excellent example of what is to be observed in the case of more or less tall and 

 columnar trunks, doubtless uniformly embedded in a horizontal position in soft 

 sandstones. The type of C. ingens (cf. plates 1 and 11), a large and superbly con- 

 served trunk w r ith finely preserved bisporangiate strobili and a partially emergent 

 crown of leaves with all their characters indicated, is strongly flattened, as better 

 shown on plate II, without any very noticeable distortion of any of its parts. Some 

 bases of trunks of this same species are, however, so //early cylindrical that we must 

 regard the lateral compression of the greater number as secondary. Likewise in the 

 case of the more numerous series of specimens assigned to C. Jewieyana, while the 

 greater number are more or less compressed, not a few, including some trunks of 

 the largest size, are so nearly cylindrical as to require close measurement to detect 

 any slight transverse elliptieity that may be present. Another Black Hawk species 

 with columnar trunks, but remarkable for the small size and great number of its 

 leaf bases with but slight development of ramentum, is C. rhombica. No one could 

 mistake specimens of this clearly distinct species ; yet, of the two good examples, 

 Nos. 625 and 623 of the Yale collection, the former is strongly compressed, while 

 the latter is perfectly cylindrical. On turning now to certain of our American 

 specimens which must be included in the genus Benncttites, if valid, and which 

 agree most closely with the English specimens, the same facts are observed. The 



