CHAPTER IV 

 CYCADOPHYTES— CYCADALES 



All the forms described in previous chapters arc extinct. The Cy- 

 cadofilicales had already begun to decline before the end of the Car- 

 boniferous, so that it was a dwindling group which struggled through 

 the Triassic and touched the Jurassic. The Bennettitales were domi- 

 nant in the Jurassic, even forming forests, if a dense vegetation of 

 such small plants could be called a forest; and well into the Creta- 

 ceous they were still abundant. But none of them persisted until 

 the end of that period. 



The Cycadales, like the Bennettitales, were derived from the 

 Cycadofilicales, probably being differentiated from that group in the 

 later Carboniferous. Consequently, throughout the Mesozoic, until 

 the Bennettitales became extinct, the two groups must have been 

 growing side by side. Why are the Cycadales so scantily represented 

 as fossils, while the Bennettitales are so abundant? The strobili of 

 the Cycadales usually begin to decay as soon as they reach maturity. 

 Sometimes, under dry conditions, the cones shrivel and become very 

 hard; but under such conditions, fossilization is unlikely to take 

 place. Of course, the leaves are practically identical in the two 

 groups, so that it is quite possible that some of the unattached leaves 

 which have been assigned to the Bennettitales really belong to the 

 Cycadales. The trunks also are often very similar, and the resem- 

 blance Would be most striking when the Cycadales trunk bore nu- 

 merous axillary strobili. 



Neither the Bennettitales nor the extinct members of the Cyca- 

 dales have left any fossils of such great size as some of the living 

 Cycadales; for many reach a height of 2 meters, while 4 or 5 meters 

 is not rare, and occasional individuals have been measured up to a 

 height of 18 meters. 



While the Cycadales have not left as complete a record in the 

 rocks as we might wish, still, there is enough to prove their presence 



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