DIFFERENCES AND APPROXIMATIONS 493 
that merely compare the relative numbers in existing lists. 
This is one of the cases where Hooker, after raising all the 
possible objections which must be overcome, is himself con- 
verted to Darwin's view by the facts which he has elicited for 
him. 
He vehemently repudiates the notion (suggested by a 
geological article) of coal having been formed in shallow seas, 
and about this Darwin long continues to poke fun at himself 
and the botanists, to whom he finds it is the proverbial red 
rag. They differ as to continental extensions. While both 
condemn Forbes' unrestrained speculations in this direction. 
Hooker is too hberal for Darwin, who, though on occasion 
claiming and accepting great geological changes in land and 
sea, stands out against volcanic islands in the ocean being 
thus linked to continents, or the invocation of vast upheavals 
and depressions without other and independent evidence, 
as a simple way of accounting for a single phenomenon in 
distribution. Later, however, we see him constrained to 
accept Hooker's claim for a continental extension to New 
Zealand, as one of the cases that ' required it in an eminent 
degree,' but through a vanished Antarctic land, not directly 
to Australia. 
Meantime he debates with his friend every other possible 
form of transport. Seeds may be carried by winds, ocean 
currents, berg transport, in mud clinging to a bird's foot, m 
the crops of birds, even the most unexpected birds, as when 
to his triumph a petrel is found helping in the transport of 
certain nuts. He confounds the popular behef that seeds 
of every kind must inevitably be destroyed by immersion 
in sea-water, through a series of experiments on temperate 
and tropical seeds, the latter suppHed often from Kew, where 
also some of the experiments are repeated. He makes a 
salt-water tank, and tests the power of seeds to sink or swim, 
discovers how many will germinate happily after this treat- 
ment. He tells how his children at Down anxiously watch 
the trials to see whether he will ' beat Dr. Hooker.' Then as 
the experiments proceed and a seed to be experimented on 
happens to be delayed, he chaffs his friend merrily : * I 
