206 AMERICA : GEOGEAPHICAL DISTRIBUTION 



results in the great mountain chains of the West, where now 

 only a few botanical ' pockets ' of East Asiatic type exist, 

 among plants of Mexican and more southern types ? Unsup- 

 ported suggestions had been advanced of contemporary sub- 

 mergence of these high lands or of recent unsuitable climate ; 

 actual investigation was to show that these ' pockets ' extended 

 over specially favoured areas. Considering that the high 

 mountains would have kept the glacial cap long after it had 

 retired from the other levels of North America, the plants 

 of East Asiatic type could have got no foothold there save in 

 these favoured areas, and by the time that the general change 

 of climate had melted this belated ice-cap, it would also have 

 affected the now treeless prairie district, exterminating these 

 plants and leaving the survivors isolated in the more congenial 

 forest district of the Eastern States, with no possibility of 

 re-invading the Rocky Mountain area, which was thus left 

 open to the plants advancing from the Mexican highlands until 

 they met, not temperate, but Boreal forms. 



The Polar problem in its relation to the whole question 

 of distribution was constantly before Hooker's eyes, and it 

 has been noted that in 1873 he was working in this connexion 

 at the flora of North- West America. 



The journey this time, though often beyond beaten tracks, 

 could not class with the wholly adventurous trips which had 

 so strongly appealed to his spirit in earlier days, and which 

 he had renounced after his Marocco expedition. Still there 

 was a flavour of the elemental joy and labour of the wild that 

 might not have been welcome to every man of sixty. The 

 two elderly botanists were indefatigable, and Hooker especially, 

 who never carried a superfluous ounce on his bones, astonished 

 the rest of the party by his activity, though his own remark is; 

 ' Gray is a man of extraordinary energy, and though 5 or 6 

 years my senior is the younger of the two ! ' 



After seeing his daughter married on June 23, Hooker 

 sailed for New York on the 28th. Professor Dyer was to 

 return in a 'week to 'carry on' until his chief came back. 

 when he would be free to take the rest of his honeymoon. 



With him went his old friend Major-General (Sir) Richard 



