﻿PRESERVATION AND EXTERNAL CHARACTERS. 



31 



reaches a height of 20 to 23 meters and a maximum diameter of nearly 1 meter. 

 In the fossil forms no such a relatively considerable size is indicated, the existence 

 of trunks exceeding 2 meters in height only being inferential — the great majority 

 of forms not reaching more than a few feet in length, although exhibiting some 

 highly interesting types of branching. 



We may next take up in more 

 detail some of the most important 

 fossil trunk types, beginning with 

 the mouaxial and smaller forms. 



LOW-GROWING UNBRANCHED TRUNKS. 



Only among the cycads from 

 the Black Hills do we find numer- 

 ous and well-marked branching 

 trunks. But the frequency with 

 which such trunks occur there, 

 when taken together with the rarity 

 of branching trunks in most other 

 localities, is partly due to the fact 

 that branches are likely to be broken 

 apart and scattered during the course 

 of erosion from the containing beds, 

 so that we fail to observe what was 

 the true habit in this respect. Thus 

 Lignier (84) is of the opinion that 

 the type specimen of Cycadeoidea 

 micromyela may well have been a 

 small branch of a larger trunk. 

 Among the living cycads the low- 

 growing trunks of Stangeria and 

 Bozvenia, as well as many species 

 of Zamia, are not much given to 

 branching ; and likewise among the 

 fossil forms small, simple-stemmed 

 and low-growing,though apparently 

 mature trunks, are present in nearly 

 all localities, being in a few the characteristic type. Of course, only where a con- 

 siderable number of specimens are present can we reach any conclusion as to what 

 the limits of size are. The most typical series of pygmy and, so far as we can say, 

 unbranched trunks, is that from Carbon County, Wyoming, upon which Professor 

 Ward has based his genus Cycadella, as so profusely illustrated in the Status of the 

 Mesozoic Floras (178). The average size of these specimens is usually about 35 

 cm. in height by 20 cm. in diameter, or scarcely more than a fourth of the bulk of 

 the Black Hills specimens of Cycadeoidea. The next larger series of simple-stemmed 

 trunks is well displayed in the Maryland Cycadeoideae, which are mostly interrne- 



Fig. 6. — Bowenia spectabilis. 

 Ovulate plant, subterranean, tuberous ; only existing cycad with bipin- 

 nate fronds. Much reduced to the right ; to the left, cone half 

 natural size, a, megasporophyll ; b, staminate cone, with micro- 

 sporophylls in inferior, superior, and lateral view at c, d, e. From 

 Engler and Prantl, after Bot. Mag., PI. 6008. 



