316 Transactions. — Botany. 



been a narrow piece of water to cross. If, however, a 

 large area containing an abundant plant population becomes 

 by degrees much restricted the struggle for existence must 

 become much keener, and only those plants can survive, 

 as certain stations become of very limited area, which can 

 drive their competitors out of such stations ; or. if themselves 

 forced to move elsewhere, possess powers of rapid adaptation 

 to the new conditions ; or, what is often more important, 

 some structure designed primarily for another purpose may, 

 being put to a secondary use, enable them to hold their own 

 in another station. Under the above circumstances many 

 plants must be eradicated altogether, and others must take 

 refuge in the most inhospitable places, while others, again, 

 may easily occupy a quite different station from that to which 

 they are accustomed. According to this view, the species of 

 plants in the Chatham Islands must have decreased enor- 

 mously in numbers since the time when the Ghathams formed 

 part of Greater New Zealand." 



How a very slight change in edaphic and climatic condi- 

 tions can affect the vegetation of Chatham Island is exhibited 

 by the two distinct regions of vegetation, the tableland and 

 the lowland, each of which contains plants unknown or 

 very scarce in the other. With quite a small modification of 

 the above conditions numbers of plants would perish. 



Several plants are extremely local ; for instance, Gunnera 

 monoica has been found in only one place in Chatham Is- 

 land (11), although the ground in many places would seem to 

 be an ideal station for it. There seems no reason why there 

 should be only a very few trees of Goprosma robusta on the 

 island when G. cliathamica is one of the commonest trees. Dis- 

 caria toumatou, found now in one or two places, should surely 

 have become established on the fixed sand-dunes ; but these, 

 being suitable for forest growth, would not allow it to occupy 

 what is a characteristic habitat in New Zealand. Other trees 

 or shrubs of very limited distribution are Dodoncea viscosa, 

 Myoporum latum, Leptospermum scoparium, and Plagianthus 

 divaricatns. Make the tableland a little wetter and Olearia 

 cliathamica would become simply a rock plant, and with the 

 weathering of the rock on which it grew might be eradicated. 

 Reduce the level of the island a few metres and Sophora 

 would exist no longer. Bearing facts such as the above in 



* For a different view of the case, see Mr. Cheeseman's paper on the 

 "Flora of the Kermadec Islands " (6). The occurrence on Chatham 

 Island of Goprosma cliathamica, so closely related to C. ■petiolata of the 

 Kermadecs, and of Ehopalostylis baueri in both regions, if the iden- 

 tification of the latter be correct, suggests that they travelled along the 

 coast, which would, in the event of an east and north-east extension of 

 New Zealand, join the Kermadecs and the Chathams. 



