HOOKER LECTURE, 1922. 221 
Fernandez. The latter island is also the home of T'hyrsopteris elegans, a 
Fern which occurs nowhere eise in the world : is this species a new creation 
which has not had time to spread, or is it the last of a long line of ancestors 
which in a former period of the earth's history occupied a much more 
extended territory? Thyrsopteris is very closely allied to certain Jurassic 
Ferns from the Yorkshire coast and many other places: geological evidence 
points to a remote antiquity, and its present isolation is in all probability the 
last phase in the history of a direct derivative of a widely scattered Jurassic 
type. 
Though by no means unrepresented in desert regions, Ferns are in the 
main mesotherm hygrophytes : several families include markedly xerophilous 
representatives, and even the Maidenhair Fern, Adiantum Capillus- Veneris, 
grows in sheltered and moist places in the arid regions of Mesopotamia and 
Central Asia. It is in the moist atmosphere of tropical and sub-tropical 
islands that Ferns reach their richest development. It has been stated that 
Ferns are particularly sensitive to climate and therefore valuable as climatic 
indicators. While admitting that existing Ferns are as a whole associated 
with certain types of habitat, the capacity exhibited by several species for 
enduring strongly contrasted conditions detraets from their value in 
enquiries into the climates of the past. 
Dr. Willis, whose contributions to the subject of geographical distribution 
have deservedly attracted much attention, admits that there are exceptions 
to his general law of Age and Area which classes species and genera of 
restricted range among the more recent products of evolution ; but thoroughly 
to appreciate the inward meaning of distribution, regard must be had to past 
history. Intimately connected with enquiries based on phytogeographical 
data are questions of inter-relationships of genera and families. The 
researches of Prof. Bower enable us to acquire a clearer conception of the 
natural classification of Ferns. He believes that ** the most positive line we 
possess in the broad avenue of botanical phylesis is that of paleeophytology.” 
Without a strict application of what he happily calls the paleontological 
check we cannot interpret phytogeographical facts with much hope of 
satisfactory results, nor can we with any confidence assign existing families 
to their respective positions in an evolutionary sequence. In the words 
of a seventeenth century divine, “ without history a man’s soul is purblind, 
seeing only the things which almost touch his eyes.” 
My aim is to connect as clearly as may be the Past with the Present 
without over-emphasising the boundary between what is and what was. If 
we confine ourselves to the Present the plant world appears to be in an 
almost static condition : viewed by itself it produces no impression of change 
on a large scale; but imagination has fuller scope when among the relics of a 
bygone vegetation we discover strange types that stimulate our faney, and 
evolution becomes a relatively rapid process. ‘The linking up into series of 
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