October 8, 1903] 



NATURE 



56; 



in succeeding ages the group rapidly increased in number 

 and variety until, 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 in- 

 dication of our ignorance of their reproductive organs, or 

 of the anatomical structure of their stems. As Prof. 

 Nathorst has recently suggested, it is convenient to speak 

 of these Cycadean remains as belonging to the group 

 Cycadophyta. On the other hand, we find numerous 

 petrified stems bearing well-preserved reproductive organs 

 ■Arhich enable us to compare the extinct with the existing 

 jpecies. We are in possession of enough facts to justify 

 the statement that the majority of Mesozoic Cycads bore 

 reproductive organs which differed in important morpho- 

 logical characters from those of existing forms. The re- 

 searches of Williamson, Carruthers, Solms-Laubach, 

 Lignier, and others, have revealed the existence of a large 

 group of Cycadean plants — known as the Bennettiteae — 

 almost identical in habit with modern sago-palms, but dis- 

 tinguished by the complexity of their reproductive shoots. 

 The Bennettiteae, originally founded on a petrified stem dis- 

 covered more than fifty years ago in the Isle of Wight, 

 and represented by another fossil which Carruthers made 

 the type of a new genus, Williamsonia, in 1870, possessed 

 a thick stem, clothed with an armour of persistent leaf-bases 

 and bearing a crown of pinnate fronds, as in most modern 

 Cvcads ; but their flowers, which were borne on lateral shoots, 



Maidenhair-tree of China and Japan. Ginkgo (or Salis- 

 buria) biloba 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 living 

 Maidenhair-tree is in truth an anachronism, a solitary 

 remnant that brings us into touch with a vanished world 

 and appears as an alien among its modern associates. The 

 abundance of fossil leaves, like those of Ginkgo biloba, 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 Gink- 

 goales during the Rhaetic, 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 existing species. The abundance 

 of fossil Ginkgoales in other parts of the world — in 

 Australia, South Africa, South America, China, Japan, 

 North America, Greenland, Franz Josef's Land, Siberia, 

 and throughout Europe — demonstrates the former vigour of 

 this class of plants of which but one member survives. 

 I'his type of Gymnosperm is distinctly foreshadowed in the 

 Palaeozoic vegetation, and as recently as the Eocene period 

 a species of Ginkgo, indistinguishable in the form of its 

 leaves from the living Maidenhair-tree, flourished in 

 Western Scotland. 



The accompanying table of distribution shows how ex- 

 tensive was the range of the Ginkgoales in the Mesozoic 

 era — both geographically and stratigraphically. 



Geographical Distrioutioii of the Ginkgoales. 



were more highly specialised than those of the true Cycads. 

 W hile most of the Mesozoic Cycads were no doubt members 

 of the Bennettiteae, others appear to have possessed re- 

 productive organs like those of recent species. The 

 Bennettiteae belong to that vast army of plants that 

 succumbed in the struggle for existence aeons before the 

 dawn of the Recent period. The other section of the 

 Cycadophyta, the Cycadaceae, still lingers on as one of the 

 select band the present insignificance of which constitutes a 

 badge of ancient lineage, and a faint reflection of past 

 supremacy. 



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 first discovery of petrified Cycadean stems in America 

 was made by Tyson in 1859, who found two specimens in 

 the Potomac beds of Maryland ; since then more than 700 

 trunks, remnants of a vast Cycadean forest, have been 

 obtained from the Black Hills alone. The investigations 

 •^'f Mr. Wieland, of Yale, who has been engaged for some 

 • ' on the examination of this rich material, have already 

 > aled the fact that in some of the Bennettiteae the male 

 ...I I 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. We have watched the progress of Mr. Wieland 's 

 researches with keen interest and look forward to further 

 important developments. With some of us, indeed, the 

 feelings of the ideal student of science are in danger of 

 bein?' overshadowed by a sensation akin to envy and a 

 desire to invade American territory. 



c. Ginkgoales. 

 Before leaving the Gymnosperms a word must be said 

 about another section — the Ginkgoales — represented by the 



NO. 1 77 1, VOL. 68] 



d. Ferns. 



Although many of the Mesozoic ferns are preserved only 

 in the form of sterile fronds and are of little botanical 

 interest, several examples of fertile leaves are known which 

 it is possible to compare with modern types. The Poly- 

 podiaceae, representing the dominant family of recent ferns, 

 are met with in nearly all parts of the world and possess 

 the attributes of a group of plants at the zenith of its pros- 

 perity. We may confidently state that so far as the some- 

 what meagre evidence allows us to form an opinion, this 

 family occupied a subordinate position in the composition 

 of Mesozoic floras. Polypodiaceous sporangia have been 

 met with in Paljeozoic rocks, and their existence during the 

 Mesozoic period is not merely a justifiable assumption, but 

 is demonstrated by the occurrence of undoubted species of 

 Polypodiaceae. It seems clear, however, that this family 

 did not attain to a position of importance until the Mesozoic 

 vegetation gave place to that which characterises the pre- 

 sent period. The Osmundaceae are now represented by five 

 species of Todea and four of Osmunda ; Todea barbara 

 occurs in South Africa, Austral' ,. Tasmania, and New 

 Zealand, the other species are al. Imy ferns and occur in 

 New Zealand, New South Wales, i"Jew Caledonia, Samoa, 

 and in a few other southern regions. The genus Osmunda 

 has a wider range, occurring in Europe, Asia, North 

 America, India, Japan, Southern China, Java, South Africa, 

 and other parts of the world. During the Rhaetic and 

 Jurassic periods the Osmundaceae flourished over the greater 

 part of Europe ; their remains have been recorded from 

 England, Germany, Scandinavia, Russia, Poland, Siberia, 

 and Greenland, also from North America, Persia, and 

 China. 



Similarly the Schizaeaceae, a family now represented by a 

 few genera in India, North America, South America, Africa, 

 Australia, Japan, China, and elsewhere, were among the 

 more abundant ferns in the Jurassic vegetation. The 

 Cyatheaceae, a family that is now for the most part con- 

 fined to the tropics, constituted another vigorous and widely 



