14:2 MORPHOLOGY OF SPERMATOPHYTES 



BENNETTITALES 



Cordaitales were the dominant Paleozoic Gymnosperms,. 

 and associated with them were the numerous Cycadofilices, 

 whose synthetic character is indicated by the name. The true 

 Cycadean type, however, does not become apparent until the 

 Mesozoic; and all through that age, from the Triassic to the 

 Lower Cretaceous, there was an extraordinary display of Cyca- 

 dean forms. In anatomy and general vegetative characters the 

 resemblance to living Cycads is undoubted, but in the ma- 

 jority of cases the spore-producing structures are remarkably 

 different. These so-called anomalous Cycadean forms of the 

 Mesozoic have been taken to represent a fifth great Gymno- 

 sperm phylum, which constituted the dominant vegetation of 

 the Mesozoic, much as the Dicotyledons dominate the flora 

 of to-day. 



The remains of Bennettitales have been found in abundance 

 in the explored regions of both hemispheres, and they have been 

 described under a variety of generic names, Bennettites, Cycade- 

 oidea, and Cycadella being the principal ones. The trunk is of 

 the tuberous type, and is covered by an armor of closely imbri- 

 cated persistent leaf bases. This character, together with the 

 histological details of the stem tissues, the arrangement, form, 

 and anatomy of the leaves, all have their counterpart in living 

 Cycads. In two important respects, however, the Bennettitales 

 differ from the Cycadales in external features. One is in the 

 occurrence of numerous short, lateral, and probably axillary 

 shoots which bore the inflorescence ; the other is in the presence 

 of scalelike hairs, which were packed between the leaf bases 

 and about the inflorescence and its bracts, and resemble the so- 

 called " ramenta " of Ferns rather than any known structure in 

 Cycadales. The course of the leaf traces in Bennettitales differs 

 decidedly from that in living Cycadales. In the latter, two 

 bundles leave the stele near together, " and curving in opposite 

 directions pass nearly halfway round the stem, thus entering 

 the leaf base on the opposite side from their starting points." 

 Scott 6 describes the leaf traces in Bennettitales as follows: " A 

 single bundle leaves the ring, starting from the lower angle of 

 one of the meshes. ... As the leaf trace passes out through the 

 cortex, it assumes a horseshoe form, with the concave side in- 



