﻿34 INTRODUCTORY. 



few feet apart. Similarly it would appear from the occurrence and character of the 

 specimens from Black Hawk, by far the greater number of which have been referred 

 by Professor Ward to Cycadcoidea Jenneyana, that this species must have reached a 

 considerable height. The fact that no complete trunk belonging to it has yet been 

 obtained, and that among more than one hundred complete specimens more or less 

 certainly referable to it there are only two summits, both being well preserved, 

 indicates that we have here to deal with forms reaching a length of several meters. 

 Moreover, among the Yale specimens, No. 101, although a meter in length and a 

 half meter in diameter, represents only a middle segment of a trunk and is without 

 tapering. Again, Yale specimen No. 102 represents a handsome cylindrical base 

 36 cm. in height by 46 cm. in diameter, while No. 551 is a quite similar basal 

 section, without tapering above, and 50 cm. in height. The latter specimen is also 

 approximately 50 cm. in diameter, which is doubtless the maximum of this measure- 

 ment. The two summits mentioned above are remarkably alike, each measuring 

 45 cm. in height by 40 cm. in greatest diameter. Tapering slowly, they hence 

 show that they have belonged to distinctly columnar trunks. Moreover, none of 

 the specimens that can possibly be referred to C. Jenneyana show any evidence 

 of branching. Also, the least assignable length of C. Jenneyana type is given by 

 Professor Ward as 1.30 meters, whence this species is the tallest of known cycads, 

 not only from direct inference but as actually determinable from known specimens. 

 Regarding the approximate maximum height of this species as based on the actual 

 length and form of the various incomplete specimens reaching the maximum diam- 

 eter of half a meter, we may — beyond reasonably assigning a height of 2 meters — 

 only conjecture, though some further evidence is furnished by a series of fragments 

 suggesting that they originally belonged to a trunk of very considerable height. At 

 the Cycad Valley locality north of Black Hawk the writer found associated with 

 one of the C. Jenneyana summits above mentioned many additional fragments 

 clearly belonging to the same trunk as the summit and scattered over the surface of 

 the ground for a considerable distance, much as in the case of the broken Aran- 

 carioxylon trunks so numerous in the same locality and horizon. 



It can only be said, therefore, that C. Jenneyana was, as compared with other 

 Mesozoic cycads, easily the tallest known species, possibly reaching a height of 3 

 or 4 meters. But there is no reason to suppose it very likely that a height of 8 or 

 10 meters could have been reached or that by any possibility any of these stems 

 could have even approached an)- such great height as that of 20 meters attained by 

 Cycas Normanhyana. The tallest of the stems seem rather to have compared quite 

 closely in size with such genera of the Zamis as Macrozamia and Encepkalartos, 

 reaching an average height, respectively, of 2 and 3 meters. They hence fall far 

 behind the proportions reached by the great trunks of Cycas revoluta cultivated in the 

 grounds of the temple Ryugeji in Shizuoka prefecture, about 120 miles west from 

 Tokio. These cycads, as I am informed by Ikeno, are the largest and tallest yet 

 known in Japan, one trunk of the group being 8 meters in height and another 6 

 meters in height, with the enormous diameter of 1.6 meters. A figure of the entire 

 group faces page 21, 



