﻿PRESERVATION AND EXTERNAL CHARACTERS. 33 



With these low-growing, robust trunks also belong such Purbeck species as C. 

 megalophylla and microphyUa ; and it may be said in conclusion that the majority 

 of fossil cycadean trunks are of a low, conical, and robust habit, not exceeding a 

 half meter in height and a third of a meter in diameter. 



SHORT COLUMNAR TRUNKS. 



Of short columnar trunks there are a considerable number, varying in size from 

 the trunks just considered to a meter or over in height. The first to be mentioned 

 are represented in the Black Hills by the species C rhombica (plate v, photo. 4) and 

 C. Stillwelli (plate VI, photo. 4), not known from complete trunks, but of very reg- 

 ular cylindrical habit and with infrequent lateral fructifications. Also, some of the 

 Minnekahta, South Dakota, specimens, with fruits so much like those of Bennett ites 

 Gibson iaw/s, are medium-sized trunks over 50 cm. in height and about 25 cm. in 

 diameter. Next are the Maryland and Italian trunks C. Uhleri and C. Rainneriana, 

 which so markedly resemble the recently described C. nigra (178), supposed to have 

 reached a meter in height. The trunk C. excelsa from the Black Hills Rim was 

 certainly a meter in height and about 25 cm. in diameter, being comparable to 

 the strikingly similar Purbeck stem C. gigantea Seward, with a height of 1.18 

 meters and a girth of 1.07 meters. Doubtless the far more robust C. Reichenbachiana 

 approached both these specimens in height. Hence these several trunks compare 

 quite closely in height with the existing genus Dion. 



COLUMNAR TRUNKS DISTINCTLY MORE THAN ONE METER HIGH. 



In his restoration of Williamsonia gigas, Williamson has indicated this plant 

 as of tall habit, supposing it to resemble the modern Cycas, as may well have 

 been the fact. But it is to be emphasized that the restoration is based on parts of 

 associated casts of trunks, about 60 cm. in length and 10 cm. in diameter, so that all 

 we can actually say is that some of the Williamsonias from Hawkser and Runswick 

 were probably of relatively taller and slenderer habit than most of the Cycadeoideee. 

 The tallest known unbranched and complete Mesozoic trunk is Cycadcoidea gigantea 

 Seward, just mentioned as 1. 18 meters in height ; but direct evidence of trunks much 

 more than 1 meter in height is afforded by the American specimens from Black 

 Hawk, which have been referred to Ward's Cycadeoidea Jenncyana. 



Obviously in localities where the only specimens obtained have slowly weath- 

 ered out of the strata in which they were embedded, complete, tall tree-trunks are 

 not likely to be recovered, even though portions of such be present in abundance. 

 Especially is this true where the broken and disengaged parts slowly settle down 

 over steep slopes or are mixed among the debris of a talus. Thus the silicified 

 trunks of the tall-growing Araucarioxylons (of which there are such vast numbers 

 in the cycad-bearing horizons of the Black Hills Rim, where talus conditions are 

 the rule) are seldom found in lengths of more than a few feet, but are occasionally 

 seen in succession along the hill-slopes, much as if they had been broken from the 

 same trunk 50 or even more than 100 feet in length, the loose order of the parts 

 being quite like that seen after woodmen cut a long, large log into lengths which 

 roll first to one, then to the other side, or lie sometimes close together, sometimes a 



