NOTE 



The present critical review of our knowledge of the two Devonian 

 land floras was one of the last pieces of work which my husband 

 undertook. Both text and illustrations are embodied in this 

 book substantially as he left them. His health was already 

 failing when he finished the manuscript in January, 1918 — six 

 months before his death — but his delight in his subject remained 

 unabated. I do not think that anything in his scientific life gave 

 him a keener intellectual pleasure than the development of the 

 idea — the Leitmotiv of the present essay — that the transition 

 from the Algae to the Vascular Cryptogams no longer remains 

 a matter of jDure conjecture, but that, in the fossil plants of the 

 Devonian rocks, we witness, actually occurring beneath our eyes, 

 the passage from the Thallophyta to the Cormophyta. He 

 welcomed this conclusion as exemplifying a generalisation to 

 which his experience in research had gradually led him — namelj% 

 that although the apj)arent insolubility of a problem may be 

 for many years unhesitatingly ascribed to lack of data, yet, when 

 the solution is found, it often becomes obvious that the essential 

 data were all the time under one's hand, and that it was merely 

 the recognition of their significance that was lacking. 



Since the Author left this memoir as a first draft which he 



was never able to revise, I must assume the responsibility for 



its final form. I am deeply indebted to Dr D. H. Scott, F.R.S. — 



who during my husband's life-time was closely associated with 



f^ his study of the Devonian floras— for reading the manuscript 



C'^ and proofs and suggesting a number of emendations, and for 



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