204 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 
samme in the northern and southern temperate zones and on the moun- 
tains of the intermediate tropical regions.”' 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 
elves 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.” 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. 757. 
