DIFFEKENCES AND APPKOXIMATTONS 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 liberal 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, in 

 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 belief 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 supplied 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 



