2o 4 SPENCER MOORE [September 



in the north, " then," he says, " in the regular course of events the 

 southern hemisphere would in its turn be subject to a severe glacial 

 period, with the northern hemisphere rendered warmer ; and then the 

 southern temperate forms would invade the equatorial lowlands. The 

 northern forms which had before been left on the mountains would 

 now descend and mingle with the southern forms. These latter, when 

 the warmth returned, would return to their former homes, leaving some 

 few species on the mountains, and carrying southward with them some 

 of the north temperate forms which had descended from their mountain 

 fastnesses. Thus we should have some few species identically the 

 same in the northern and southern temperate zones and on the moun- 

 tains of the intermediate tropical regions." x Now we have as much 

 right to assume that glaciation first affected the southern hemisphere ; 

 and a clear idea of the result will be gained if the reader will sub- 

 stitute " south " for " north," and vice versd in the above admirable 

 quotation. Yet what a different idea of the trend of migration it 

 gives us ! 



But my imaginary opponent now proposes to crush me with an 

 argument he has carefully held in reserve. " Consider," he exclaims, 

 " the evidence furnished by introduced plants. Wherever man settles, 

 his footsteps are dogged by Scandinavian species, which rapidly 

 establish themselves in their new home and at the expense of the 

 indigenous vegetation ; how could this happen unless there is some 

 potency inherent in northern forms over and above that possessed by 

 the southern flora ? " While admitting that a considerable number of 

 northern plants have become naturalised in southern lands, it must 

 not be forgotten that some, though a far smaller number, of southern 

 species have gained a foothold north of the equator. But in order to 

 estimate properly the value of this preponderant naturalisation of 

 northern forms, we must not be contented, although even Mr. Darwin 

 seems to have been contented, with merely drawing up lists of the 

 colonists of either hemisphere ; before ascribing any aggressive power 

 to the northern flora, we must ascertain that no other explanation of 

 the facts is possible. And firstly, we note, and it is a matter of great 

 importance, that almost all the plants naturalised in southern lands 

 are herbaceous. We may take as an example Sir Joseph Hooker's 

 list of introductions into New Zealand. 2 It amounts to 170 species, 

 of which fully half are annuals, thirteen are biennials, and over fifty of 

 the remainder, although perennial, are herbaceous. Now what has 

 happened in New Zealand since the first batch of colonists landed on 

 its shores ? The densely clothed forest-lands have been cleared to 

 make room for the herbaceous vegetation on which man depends for 

 his sustenance ; in other words, a dendritic zone has been artificially 

 converted into a herbaceous one. And not this only, but the seeds 



1 "Origin of Species," 6th ed. p. 339. 



2 "Handbook New Zealand Flora," p. 7. r >7. 



