SPERMATOPHYTES 



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 Cycadeoidca and Cycadella, and in Mexico. 



Sporophyte. — 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 {ram 01 1 ion), which are 

 packed among the leaf bases 

 and sometimes sheath the whole 



body With a feltlike mass. This Fig. 426. — Photograph of fossil trunk of 



ramentum is characteristic of Cycadeoidca, showing the tuberous body and 



r „ „ 1 • r. „ • the armor of leaf bases, wedged among which 



terns, and is often conspicuous . * .... ... 



1 may be seen numerous strobili. — Alter 



upon the trunks of tree ferns, wieland. 

 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 



