Professor A. C. Seward — Floras of the Past. 505 



In endeavouring to take a comprehensive survey of the records of 

 plant-life, we should aim at a wider view of the limits of species, and 

 look for evidence of close relationship rather than for slight 

 differences, which might justify the adoption of a distinctive name. 

 Our object, in short, is not only to reduce to a common language the 

 diverse designations founded on personal idiosyncrasies, but to group 

 closely allied forms under one central type. We must boldly class 

 together plants that we believe to be nearly allied, and resist the 

 undue influence of considerations based on supposed specific 

 distinctions. 



As a preliminary consideration, we must decide upon the most 

 convenient means of expressing the facts of geographical distribution 

 in a concise form. The recognised botanical regions of the world do 

 not serve our purpose; we are not concerned with the present 

 position of mountain-chains or wide-stretching plains that constitute 

 natural boundaries between one existing flora and another, but 

 simply with the relative geographical position of localities from 

 which records of ancient floras have been obtained. I have divided 

 the surface of the earth into six belts, from west to east. The most 

 northerly or Arctic Belt includes the existing land-areas as far south 

 as latitude 60°, comprising — 1, Northern Canada ; 2, Greenland and 

 Iceland ; 3, Northern Europe ; 4, Bear Island and Spitzbergen ; 

 5, Franz Josef's Land ; 6, Northern Asia. The Nortl Temperate Belt, 

 extending from latitude 60° to 40°, includes— 7, South Canada and the 

 northern United States; 8, Central and Southern Europe ; 9, Central 

 Asia. The North Subtropical Bell comprises the land between 

 latitude 40° and the Tropic of Cancer, including— 10, the Southern 

 States of North America; 11, Northern Africa, part of Arabia and 

 Persia; 12, Thibet, and part of China; 13, Japan. The Tropical 

 Belt, embracing the land-areas between the Tropics of Cancer and 

 Capricorn, includes — 14, Central America and the northern part 

 of South America; 15, Central Africa and Madagascar; 16, 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 includes— 20, 

 the extreme south of South America; 21, Tasmania; 22,' New 

 Zealand. 



Pke-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 Cambrian, 

 Ordovician, and Silurian strata that now form the greater portion of 

 the Welsh and Cumberland hills. 



The genus Nematophjcus, originally described by Dawson as 

 Prototaxites, and afterwards referred by Carruthers to the Alg^, 

 constitutes the most satisfactory example of a Silurian plant. This 

 genus, which has fortunately been preserved in such a manner as to 

 admit of minute microscopical examination, represents a widely 

 spread algal type in Silurian and Devonian seas. The tubular 

 elements composing the stems of some species of Nematophycus — 



