BENNETTITALES 



51 



The leaf.— The leaves of the Bennettitales and the Cycadales are 

 so similar that we doubt whether the two groups could be separated 

 on the basis of the leaf alone. In both, the dominating leaf is the 

 pinnate leaf of their fihcinean progenitors. Leaves more than once 

 pinnate are rare, found only in Bowenia in the Cycadales, and we 

 have not found any record of more than once pinnate leaves in the 

 Bennettitales, if we except the pos- 

 sibility that the synangia are modi- 

 fied pinnules. If they are modified 

 pinnules, the microsporophylls are 

 bipinnate. In Williamsonia coro- 

 nata the leaves were simple and 

 entire. 



In size, the leaves are about like 

 those of living Cycads, reaching a 

 length of more than 3 meters in 

 Cycadeoidea ingens and only about 

 6 cm. in Williamsonia coronata; 

 most of them, however, ranged in 

 size between these two. In the 

 abundant material from the Lias of 

 the Mixteca Alta of Mexico, many 

 of the leaves of Ptilophyllum and 

 Otozamites were less than 25 cm. in 

 length, and in Ptilophyllum acutifolium var. minor the leaflets are 

 less than 10 cm. long. 



The venation is "parallel," which, in this phylum, means that it 

 is dichotomous, with very little forking beyond the base of the leaf- 

 let. There are no midribs in any of the leaves, but it is interesting 

 to note that, associated with leaves of the Bennettitales in the Mix- 

 teca Alta region, there are leaflets with midribs {Stangerites oaxa- 

 censis and Sagenopteris rhoifolis var. mexicana) resembling leaflets of 

 the living African Stangeria. In this connection, it might be men- 

 tioned that a South African specimen, named Zamites, in the muse- 

 um at Grahamstown, South Africa, is hardly distinguishable from 

 the living Dioon edule of Mexico. 



The histological structure of the leaf is typically xerophyllous. 



Fig. 45. — Cycadella ramentosa: 

 transverse section of ramentum: X66. 



— After WlELAND.^80 



