SPERJ^IATOPHYTES 



185 



(2) Bennettitales 



General character. — The members of this extinct group were very- 

 conspicuous during theMesozoic, and they have been called fossil cycads. 

 In fact, the Mesozoic has been called the age of cycads, so far as plants 

 are concerned. Recent investigations have shown, however, that the 

 Bennettitales are very distinct from the living cycads. They were ex- 

 traordinarily abundant during the Jurassic, numerous remains having 

 been found in North America, Europe, and Asia, and extending into 

 the arctic regions. The richest display of forms occurs in the United 

 States (Maryland, South Dakota, and Wyoming), the conspicuous 

 American genera being Cycadeoidea and Cycadella, and in Mexico. 



Sporophjrte. — The sporophyte body is generally tuberous in form, 

 sometimes very large, but short columnar trunks (three to four meters 

 high) also occur. This stem is 

 covered by a heavy armor of 

 leaf bases, among which there 

 are wedged numerous short 

 axillary branches, each bearing 

 a terminal strobilus (fig. 426). 

 The occurrence of numerous 

 strobili on lateral branches is in 

 striking contrast with the usually 

 solitary terminal strobilus of the 

 cycads. A second striking ex- 

 ternal feature is the occurrence 

 of an abundance of membranous 

 scales (ramentum), which are 

 packed among the leaf bases 

 and sometimes sheath the whole 

 body with a feltlike mass. This 

 ramentum is characteristic of 

 ferns, and is often conspicuous 

 upon the trunks of tree ferns. 

 The anatomy of the stem is 



exactly like that of the cycads ; with a very thick cortex, a compara- 

 tively thin vascular cylinder, and a large pith. The vascular bundles 

 composing the cylinder are collateral, with the protoxylem in contact 

 with the pith (endarch). In the leaves, however, the protoxylem 



Fig. 426. — Photograph of fossil trunk of 

 Cycadeoidea, showing the tuberous body and 

 the armor of leaf bases, wedged among which 

 may be seen numerous strobili. — After 



WlELAND. 



