150 MORPHOLOGY OF SPERMATOPHYTES 



dwarf shoots, the synangia, the remarkably modified and com- 

 plex ovulate strobili, the occasional bisporangiate strobili, and 

 the entire replacement of endosperm by an embryo which devel- 

 ops without a suspensor, are characters which strongly confirm 

 the suggestion that the group should be regarded as one of the 

 main divisions of the Gymnosperms. 



CYCADALES 



During the Mesozoic, along with the Bennettitales, the 

 Cycadales undoubtedly existed, but the evidence is scanty. The 

 reputation of the Mesozoic as " the age of Cycads " seems to have 

 come rather from the abundant remains of Bennettitales. Cer- 

 tain remains may be taken fairly to represent Cycads, and doubt- 

 less numerous extinct genera of Cycads may have existed, but 

 no modern genus seems to have an unclouded title in the Meso- 

 zoic except Cycas, which has been recognized in the Rhaetic 

 beds between the Lias and the Trias. The antiquity of Cycas 

 confirms morphological opinion concerning it, as it is well sepa- 

 rated from the other Cycads in features which are recognized 

 as primitive. 



GINKGOALES 



The characteristic foliage of Ginkgo makes it easy of recog- 

 nition, although some forms which have been referred to it may 

 prove to be Ferns. However, putting together the evidence of 

 foliage, flowers, and seeds, it is evident that the group was a very 

 widespread one in the Jurassic, and that the testimony is very 

 strong for claiming its existence during the Paleozoic. The in- 

 definiteness of its occurrence in the Paleozoic is based upon the 

 fact of its association with the great group Cordaitales, into 

 which it seems to merge. The conclusion reached by Scott 6 

 is as follows : " On the whole, the sum of the fossil evidence is 

 of sufficient weight to prove the great antiquity of the gymno- 

 spermous family now represented by the Maidenhair tree, which 

 appears to be best regarded as the one surviving member of an 

 ancient stock, derived from the same cycle of affinity as the 

 Paleozoic Cordaiteae, once the dominant type of Gymno- 

 sperms. 77 



