A EATIONAL HYPOTHESIS 509 
this of the simplest organism, because it would commit him to 
the doctrine of spontaneous generation of organisms of every 
degree of complexity. 
If the barren facts under such a theory may receive a 
rational explanation under another theory, the naturahst 
should use this as the means of penetrating the mystery of 
the origin of species, holding himself ready to lay it down 
when it shall prove as useless for the further advance of 
science as the long serviceable theory of special creations, 
founded on genetic resemblance, now appears to be. 
Only the application of these principles could explain ration- 
ally the apparent anomalies of the Australian Flora, its ancient 
types reinforced by European migrants whose course could be 
traced along the intermediate highlands, and its two southern 
corners, only recently joined by the rise of the barren land 
between, possessing each the remains of separate floras de- 
veloped on different portions of a large but now vanished 
Antarctic continent. 
The Tasmanian Introduction was for the scientific world 
only. Hooker was right in his estimate of its popularity, though 
wrong about the ' Origin,' which had an unimaginable success, 
the first edition being sold out at once on the day of pubhca- 
tion, November 24. Thus he writes to Darwin in April (?) 1859 : 
From what Boott said I thought Lyell had exceeded so 
much my estimate of the pubhc's interest in such works, 
that I could not help saying so to Boott. How glad I shall 
be if it proves the contrary for Science's sake. As to my 
Essay, if Keeve does not print it separately [this was done] 
only 150 copies will be printed and 75 sold, as of the Flora 
Tasmanica ; if he does, I shall buy 100 for distribution, and 
the sale of the remainder will, judging from the New Zealand 
Essay, be 2 copies ! In point of sale or awakening interest 
our books cannot interfere — the number who read both will 
be inconceivably smaller. 
The pubHcation of the f Origin ' eHcited the following : it will 
be noted how Hooker continued to lay more stress on factors 
other than Natural Selection. 
