304 CONCLUSION 



the help of some geological reason. In other words, the 

 processes of modification of unlike plant materials in 

 view of the same end have been different. Starting with 

 a different history or heredity, plant materials evolving 

 towards a similar adjustment to similar circumstances 

 have attained this same end in different ways. Assuming, 

 therefore, an equal degree of fitness to thrive, reproduce, 

 and spread amid equivalent surroundings, it is not sur- 

 prising that the result, in point of plant-forms and 

 combinations thereof, offers divergences. It would be 

 bold, however, to assert that the vegetation, even as 

 it is now represented in corresponding natural regions, 

 is adapted with equal efficiency to its actual environ- 

 ment. Instances are not wanting of one type of 

 vegetation dying out, of another slowly spreading and 

 replacing it. 



In South Africa the mediterranean vegetation of the 

 south-western or Cape region is slowly being driven 

 back by the drier and lower forms of the Karroos : in 

 the savanas of Central Africa it is an open question 

 whether the baobab or monkey-bread tree is still 

 spreading or holding its own, indeed whether it is not 

 gradually dying out: in the back lands of Queensland 

 and New South Wales, there is a severe struggle between 

 the grass-land and the thorny brigalow scrub whose 

 formidable tangles steadily spread and kill the grass : 

 again, the superior fitness of plants, from other but 

 similar regions of the world, to hold the ground is well 

 illustrated in the Plate region, where weeds imported 

 from the Mediterranean propagate with extraordinary 

 rapidity at the expense of the native species : or again 

 in New Zealand, where a high proportion of foreign 

 plants have been able successfully to compete with the 

 indigenous vegetation. Nearer home, the advance of 



