602 



STRUCTURE AND LIFE HISTORIES 



Cycadeoidea by the celebrated geologist Buckland. The 

 name of the order is derived from the genus-name, Bennet- 

 tites. 1 Other forms, usually found as casts, are called 

 Williamsonia, still others are known mainly as genera 

 founded on leaf imprints. 



520. Cycadeoidea. In most of its purely vegetative 

 characters, such as the anatomy of the stem and the 



FIG. 423. Cycadeoidea dacotensis (?). Photomicrograph of a young 

 seed (X 15), showing a sterile scale on either side. Between them pro- 

 jects the entire length of the tube through which the micropyle extends. 

 The partially collapsed nucellus is distinctly shown in the center. (After 

 Wieland.) 



structure of the leaves, Cycadeoidea resembled modern 

 cycads, , but its reproductive branches were character- 

 istically lateral, which is one of the most fundamental 

 characteristics of the higher seed-bearing plants of to- 

 day. Only two modern cycads (Macrozamia and Bowenia) 

 have lateral seed-bearing cones (Fig. 289). 2 Various 



1 Cycadeoidea Buckland Bennettites Carruthers. 



2 The staminate cones of Zamia are lateral. 



