Cockayne. — Development of Seedlings. 281 



havens of refuge would be open to those forest -trees and 

 other plants which could not tolerate the increasing dry- 

 ness of climate, viz. : The region west of the Southern Alps 

 and of the central ranges of the North Island, and which 

 would then, as now, support a dense forest population ; the 

 warmer and moister regions of the North ; and the eastern 

 coast, part of which would include the then high lands of the 

 •Chatham Islands. These islands, having been in the Miocene 

 period below the level of the sea, would possess no inhabit- 

 ants to resist the invaders, consequently a purely Pliocene 

 vegetation would there settle down and possibly undergo little 

 -change in the equable climate, as evidenced by early seedling 

 forms of the present plants showing so great a resemblance to 

 the present adult form. How long the connection between 

 the Chathams and New Zealand existed, or whether the two 

 lands were ever actually united or separated merely by a very 

 narrow strait, geologists have not been able yet to determine. 

 It seems clear, however, that when a subsidence of the land 

 took place, then very soon the Chathams would be isolated 

 sufficiently to receive very few plant immigrants, while yet 

 steppe conditions would reign over much of eastern New 

 Zealand. Finally, the subsidence continuing, New Zealand 

 would sink, either in part or as a whole, to nearly 300 m. 

 below its present level," which would reduce the area very 

 considerably, rendering many of the mountain passes of 

 the South Island no barrierf to the intermixing of eastern 

 and western plants, while in the North Island there would 

 be less obstruction still. Between the plants of the forest 

 and those of the desert the struggle must have been fierce, 

 and the most extreme xerophytes must have perished or 

 taken refuge in the most barren places, where, indeed, 

 Ave find them at the present day, on shingle- slips, dry 

 rocks, stony plains, river-beds, &e.J In this struggle those 

 plants which had never become fully adapted to extreme xero- 

 philytic conditions, such as Plagianthus betidinus, Sophora 

 tetraptera, &c, and which possess great powers of adaptability 

 by assuming quickly either a hygrophilous or a xerophilous 

 form according to circumstances, § would, I take it, be able 

 in the struggle for existence finally to vanquish their Pliocene 

 ancestors which would oppose them in the w T est or advance 



* Hutcon, " On the Lower Gorge of the Wairnakariri " (Trans. N.Z. 

 Inst., vol. xvi., 1883, pp. 453, 454). 



f Haast Pass, Arthur's Pass, Walker's Pass, Worseley Pass, Hurunui 

 Pass, Amuri Pass, Cannibal Gorge, &e. 



\ Such plants are Carmichaelia crassicaule, Raoulia cximia and its 

 allies, the plants of shingle-slips, Ozothammu coralloides, 0. selago, 0. 

 microphyllus, 0. depressus, Epilobium crassum, Hectorella ccespitosa, &c. 



§ Several examples are to ba found in this and in my previous papers 

 •on New Zealaud seedlings. 



