558 Notices of Memoirs — 



vegetation. Before the end of the Palgeozoic era there existed plants 

 bearing pinnate fronds similar to those of recent species of 

 Cycadaceee, and in succeeding ages the group rapidly increased 

 in number and variety till, in the Jurassic and the early Cretaceous 

 periods, the Cycads asserted their superiority as the leading type 

 of vegetation. The majority of Mesozoic Cycadean fronds are 

 assigned to artificial or form -genera as an indication of our 

 ignorance of their reproductive organs, or of the anatomical structure 

 of their stems. As Professor Nathorst has recently suggested, it is 

 oonvenient to speak of these Cycadean remains as belonging to the 

 group Cycadopbyta. On the other hand, we find numerous petrified 

 stems bearing well-preserved reproductive organs which enable 

 us to compare the extinct with the existing species. We are in 

 possession of enough facts to justify the statement that the majority 

 of Mesozoic Cycads bore reproductive organs which differed in 

 important morphological characters from those of existing forms. 

 The Bennettite^, originally founded on a petrified stem discovered 

 more than fifty years ago in the Isle of Wight, possessed a thick 

 stem, clothed with an armour of persistent leaf-bases and bearing 

 a crown of pinnate fronds, as in most modern Cycads; but their 

 flowers, which were borne on lateral shoots, were more highly 

 specialised than those of the true Cycads. While most of the 

 Mesozoic Cycads were no doubt members of the Bennettiteee, others 

 appear to have possessed reproductive organs like those of recent 

 species. The Bennettitege belong to that vast army of plants that 

 succumbed in the struggle for existence eeons before the dawn of the 

 Eecent period. 



The wealth of Cycadean vegetation during the latter part of the 

 Jurassic and the earlier stages of the Cretaceous periods is admirably 

 illustrated by the discovery in the Black Hills of North America and 

 in other districts of the United States of hundreds of silicified 

 trunks of Cycadean plants. The investigations of Mr. Wieland, of 

 Yale, who has been engaged for some time on the examination of this 

 rich material, have already revealed the fact that in some of the 

 Bennettiteee the male and female organs were borne in a single 

 flower, the female portion having a structure identical with that 

 previously described from European stems, while the male flowers 

 bear a close resemblance to the fertile fronds of a Marattiaceous fern. 



C. Ginkgoales. — Before leaving the Gymnosperms a word must be 

 said about another section — the Ginkgoales — represented by the 

 Maidenhair -tree of China and Japan. Oinlcgo (or Salisbiiria) 

 hiloba has almost, if not quite, ceased to exist in an absolutely wild 

 state, but as a cultivated tree it has now become familiar both 

 in America and Europe. The abundance of fossil leaves, like those 

 of Giiikgo hiloha, and of other slightly different forms referred to 

 the genus Baiera, associated not infrequently with remains of male 

 and female flowers, demonstrates the ubiquitous character of the 

 Ginkgoales during the Ehsetic, Jurassic, and Wealden periods. In 

 the Jurassic shales of the Yorkshire coast, Ginkgo and Baiera leaves 

 occur in plenty, some of them practically identical with those of the 



