October 8, 1903] 



NATURE 



557 



Madagascar ; i6, India, the Malay Archipelago, and 

 Northern Australia. The South Subtropical Belt, extending 

 from the Tropic of Capricorn to latitude 40° south, includes 

 — 17, Central South America ; 18, South Africa ; 19, Central 

 and Southern Australia. The South Temperate Belt in- 

 cludes — 20, the extreme south of South America; 21, Tas- 

 mania ; 22, New Zealand. 



Pre-Devonian Floras. 

 The scanty records from pre-Devonian rocks afford but 

 little information as to the nature of the vegetation that 

 existed during the period in which were deposited the Cam- 

 brian, Ordovician, and Silurian strata that now form the 

 greater portion of the Welsh and Cumberland hills. We 

 must wait for further discoveries before attempting to give 

 more than the barest outline of the plant-life of these remote 

 epochs. Our knowledge of the plant-world which existed 

 during the Silurian period is far too meagre to justify any 

 statement as to geographical distribution. Of the few re- 



found in Silurian strata in Wales, Shropshire, and New 

 Brunswick ; also in Devonian rocks of Eastern Canada, New 

 York, Ohio, and North-West Germany, The tubular ele- 

 ments composing the stems of some species of Nematophycus 

 — which reached a diameter of 2 or 3 feet — exhibit a regular 

 variation in width, giving the appearance of concentric rings 

 of growth, as in the stems of the tree-like Lessonia, an ex- 

 isting genus of Antarctic seaweeds. This structural feature 

 presents an impressive image in stone of a plant's rhythmical 

 response to some periodically recurring conditions of growth 

 in the waters of Palaeozoic seas. 



Devonian and Lower Carboniferous Floras. 

 The earliest plants that have been found in sufficient num- 

 ber, and in a state of preservation which renders their iden- 

 tification possible, are those from Devonian rocks. From 

 Bear Island, a small remnant of land situated within the 

 Arctic circle, the late Prof. Heer described several Devonian 

 plants ; and more recently Prof. Nathorst, of Stockholm, has 



Map I. — The Earth's Surface divided into Areas (1-22) for convenience in recording the 

 Geographical Distribution of Fossil Plants. 



Sub-tropical 



Tropical 



Sub- tropical 



Temperat* 



cords of supposed Silurian plants, several have been shown 

 to be unsatisfactory, and the nature of others is too uncer- 

 tain to admit of accurate identification. The Lepidodendron- 

 like fossil from the Clinton limestone of Silurian age in 

 Ohio, described by Claypole in 1878 as Glyptodendron, has 

 been referred by a later writer to a Cephalopod. Stur's 

 Bohemian plants, described in 1881, are too imperfect to 

 afford any information of botanical value ; while the ferns 

 and lepidodendroid plants recently recorded by Potoni^ from 

 the Hartz Mountains are more likely to be of Devonian than 

 Silurian age. 



The genus Nematophycus, originally described by 

 Dawson as Prototaxites, and afterwards referred by Car- 

 ruthers to the Algae, constitutes the most satisfactory 

 example of a Silurian plant. This genus, which has for- 

 tunately been preserved in such a manner as to admit of 

 minute microscopical examination, represents a widely spread 

 algal type in Silurian and Devonian seas. It has been 



given a full account of this interesting and comparatively 

 rich flora. The relics of plant-life preserved in this Arctic 

 island carry us back through countless ages to a time when 

 a luxuriant vegetation flourished in a region now occupied 

 by ice-bound land and polar seas. As Edward Fitzgerald 

 said, in speaking of his enjoyment of some geological book : 

 " This vision of time is in itself more wonderful than all the 

 conceptions of Dante and Milton." Devonian plants have 

 been described by Feistmantel, Etheridge, and others from 

 Australia ; and the well-known Kiltorkan grits of Ireland 

 have supplied a few well-preserved impressions of the oldest 

 land-plants disinterred from British rocks. 



As my aim is to sketch in broad outline the general facies 

 of the vegetation which flourished at different stages in the 

 earth's history, rather than to undertake a critical examin- 

 ation of the evidence as to the precise geological age of the 

 plant-bearing beds, I propose to treat of Devonian and Lower 

 Carboniferous floras as constituting one phase in the evolu- 



No. 1 77 1, VOL. 68] 



