748 REPORT— 1900. 



homogeneous, and almost wholly siliceous, and in them a mass of presumably 

 aquatic vegetation rooted itself. This further impediment to movement in the 

 water cut off all sediment, and the material brought into the area then consisted only 

 of wind-borne vegetable dust or floating vegetable matter carrying an occasional 

 boulder. Lastly, the formation of the coal-seam was brought to a close by a sudden 

 invasion of the area by moving water. The mass of vegetable matter, often after 

 suffering some little erosion, was buried by sandstone or shale rich in large 

 drifted remains of plants or trees, and the whole process was recommenced. 



Botanical Evidence heariiig on the Climatic and other Physical 

 Conditions tender which Coal was formed. By A. C. Seward, F.R.S. 



Botanical investigations into the nature and composition of the vegetation 

 •which has left abundant traces in the sediments of the Coal-measures may be ex- 

 pected to throw some light on the natural conditi-ms which prevailed during that 

 period in the earth's history that was par excellence tue age of coal production. 

 The minute examination of petrified tissues has rendered possible a restoration of 

 the internal framework of several extinct types of plant-life, and has carried us a 

 step further towards the solution of evolutionary problems. It is possible, even 

 with our present knowledge, to make a limited use of anatomical structure as an 

 index of life-conditions, and to restore in some degree from structural records the 

 physiological and physical conditions of plant-life characteristic of the close of the 

 Carboniferous epoch. 



I. Evidence furnished by the Coal-period Floras as to Climatic and 

 other Physical Conditions, 



The uniformity in the character of the vegetation exaggerated ; the Olossopteris 

 flora of Australia, South Africa, and South America. The existence of botanical 

 provinces in Upper Paljeozoic tinies. 



A comparison of the Coal-period vegetation with that of the present day as 

 regards (i.) the relative abundance of certain classes of plants, (ii.) the geographi- 

 cal distribution of certain families of plants during the Carboniferous epoch and at 

 the present day. The importance of bearing in mind the progress of plant-evolu- 

 tion as a factor ailecting the consideration of such comparisons. The possible exist- 

 ence of a Palaeozoic Mountain flora of which no records have been preserved. 



II. The Form, HaUt, and Manner of Occurrence of Individual Plants 

 as Indices of Conditions of Growth. 



Comparison of calamites and horse-tails. Fossil forests of calamites. Psaronius 

 stems in situ and bearing roots at difierent levels, suggesting growth in a region of 

 rapid sedimentation. Vertical stems either in loco natali or drifted. Climbing 

 plants possibly represented by Sphenophyllum, some species of ferns and Medul- 

 losete. Function of the so-called Aphlebia leaves of ferns. 



III. Anatomical Evidence. 



The value of evidence afforded by anatomical features. Risks of comparison 

 between structural character of extinct and recent plants. Structure considered 

 from the point of view of evolution, as the result of adaptation to external 

 conditions, and to mechanical and physiological requirements. 



(ci) Spores and leaves. — Abundance of spores provided with filamentous or 

 hooked appendages ; adaptation of spores to floating or to wind-dispersal. The leaf 

 structure of calamites, ferns, &c. ; presence of stomata, palisade tissue, and water- 

 glands; the 'parichnos' or aerating tissue in the leaves of Lepidodendrese and 

 Sigillarieae. 



(3) Stems and roots. — Absence of annual rings of growth. The large size of 

 ■water- conducting elements connected with rapid transport (eg. Sphenophyllum') or 

 with storage of water (e.g. Megaloxylon). The chambered pith of Cordaites, 



