36 EDWARD WILBER BERRY 



MESOZOIC HISTORY 



The Mesozoic era has been called the age of conifers, and not 

 without reason. The gymnosperms are represented during this 

 time by five great groups — the Williamsoniales, Cycadales and 

 Cycadeoidales (Bennettitales) of the cycadophyte phylum, and 

 by the Ginkgoales and Coniferales of the Coniferophyte phylum. 

 Of these five groups the Williamsoniales and Cycadeoidales 

 appear to be limited to the Mesozoic: the Ginkgoales became 

 practically extinct during the succeeding era: and there are a 

 large variety of peculiar Mesozoic types of Coniferales. 



Cycadophyta 



It is but a few years since the Mesozoic cycadophytes, so 

 abundantly represented by foliage in all parts of the world from 

 the Arctic to the Antarctic, were generally accepted as represent- 

 ing true coniferous and carpellary-leaf bearing cycads not far 

 removed from existing types. Then came the discoveries of 

 Carruthers, Solms-Laubach, and especially Wieland, demonstra- 

 ting the existence of forms in vegetative habit and appearance 

 wholly cycadean, but with fructifications unique among gymno- 

 sperms. The sporophylls, instead of being solitary and terminal, 

 were borne in abundance on lateral dwarfed branches among 

 the leaf-bases, and were bisporangiate, suggesting comparisons 

 with Ranalian flowers such as those of Liriodendron or Magnolia. 



These forms are properly referable to the genus Cycadeoidea 

 although many students abroad prefer the later name of Bennet- 

 tites. These spectacular discoveries have resulted in a vast 

 amount of misapprehension among botanists, who assume that 

 the bulk of the Mesozoic cycadophytes were of this type, whereas 

 it now seems clear that the Cycadeoidales were simply a bizarre 

 side-line, stereotyped early in the Mesozoic, and without issue. 

 Their great importance rests in the fact that because of their 

 silicification at a number of localities they have furnished the 

 key to the interpretation of the much more abundant and plastic 

 group — the Williamsoniales. In these latter are represented a 

 vast plexus of forms showing great variations in size, foliage. 



