October 8, 1903] 



NA TURE 



plexity of organisation, gave place to other products of evo- 

 lution and left no direct descendants. 



Another fact that seems to stand out clearly is the almost 

 world-wide distribution of several characteristic Lower Car- 



niferous plants. The accompanying table (Table I.), based 



559 



area of land on the site of the present United States of 

 North America, stretching across Europe into Eastern 

 Asia; under the shade of their trees lived "the stupid, 

 salamander-like Labyrinthodonts, which pottered with much 

 belly and little leg, like Falstaff in his old age." The 



on the artificial divisions marked out on the map, to which 

 reference has already been made, shows how widely some of 

 the plants had migrated from an unknown centre far back 

 in a still more remote age. We are, as yet, unable to follow 

 these Devonian plants to an earlier stage in their evolution. 

 We are left in amazement at their specialised structure and 

 extended geographical distribution, without the means of 

 perusing the opening chapters of their history. 



Upper Carboniferous (Coal-measures) and Permian Floras. 



From the Lower Carboniferous formation we pass on to 

 the wealth of material afforded by the Upper Carboniferous 

 and Permian rocks. From the point of view of both 

 botanists and geologists, the fossil plants obtained from the 

 beds associated with the coal are of greater interest and 

 importance than those of any other geological period. By 

 a fortunate accident our investigations are not restricted to 

 the examination of carbonaceous impressions and sandstone 

 casts left by the stems and leaves of the Coal-period plants. 

 By means of thin sections cut from the calcareous nodules 

 of the coal-seams of Yorkshire and Lancashire, and from 

 the silicified pebbles of France and Saxony, it is possible 

 to make anatomical investigations of the coal-forest trees 

 with as much accuracy as that with which we can examine 

 sections of recent plants. The differences between the 

 vegetation that witnessed the close of the Carboniferous 

 era and that which flourished during the opening stages 

 of the succeeding Permian epoch are comparatively slight. 

 It has been demonstrated by Grand'Eury, Kidston, Zeiller, 

 Potoni6, and others, that it is possible both to separate the 

 floras of the Coal-measures from those of Lower Permian 

 age, and to use the plant species as trustworthy guides to 

 the smaller subdivisions of the Coal-measures ; but apart 

 from these minor differences, the general facies of the 

 vegetation remained fairly constant during the Upper 

 Carboniferous and Lower Permian periods. 



The vast forests of the Coal age occupied an extensive 



NU. 1771, VOL. 68] 



plants of these Palaeozoic forests seem to be revivified, as 

 we subject their petrified fragments to microscopical ex- 

 amination. Robert Louis Stevenson has referred to a 

 venerable oak, which has been growing since the Reform- 

 ation and is yet a living thing liable to sickness and death, 

 as a speaking lesson in history. How much more im- 

 pressive is the conception of age suggested by the con- 

 templation of a group of Palaeozoic tree-stumps exposed in 

 a Carboniferous quarry and rooted where they grew ! An 

 examination of their minute anatomy carries us beyond 

 the mere knowledge of the internal architecture of their 

 stems, leaves, and seeds ; it brings us into contact with the 

 actual working of their complex machinery. As we look 

 at the stomata on the lamina of a leaf of one of those 

 strange trees, and recognise a type of structure in the 

 mesophyll-tissues which has been rendered familiar by its 

 occurrence in modern leaves, it requires but little imagin- 

 ation to see the green blade spreading its surface to the 

 light to obtain a supply of solar energy with which to 

 extract carbon from the air. We can almost hear the 

 murmur of plant-life and the sighing of the branches in 

 the wind as the sap courses through the wood, and the 

 leaves build up material from the products of earth and air ; 

 products that are to be sealed up by subsequent geological 

 changes, until after the lapse of countless ages the store 

 of energy accumulated in coal is dissipated through the 

 agency of man. 



The minute structure of the wood of the Calamites, 

 Lycopods, and other trees, agrees so closely with that of 

 existing types that we are forced to conclude that these 

 Palaeozoic plants had already solved the problem of raising 

 a column of water more than loo feet in height. The 

 arrangement of the strengthening or mechanical tissues in 

 the long flat leaves of Cordaites is an exact counterpart 

 of that which we find in modern leaves of similar form. 

 The method of disposition of supporting strands in such 

 manner as to secure the maximum effect with the least 

 expenditure of material was as much an axiom in plant 



